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287 lines
10 KiB
Markdown
287 lines
10 KiB
Markdown
# jsprim: utilities for primitive JavaScript types
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This module provides miscellaneous facilities for working with strings,
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numbers, dates, and objects and arrays of these basic types.
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### deepCopy(obj)
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Creates a deep copy of a primitive type, object, or array of primitive types.
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### deepEqual(obj1, obj2)
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Returns whether two objects are equal.
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### isEmpty(obj)
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Returns true if the given object has no properties and false otherwise. This
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is O(1) (unlike `Object.keys(obj).length === 0`, which is O(N)).
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### hasKey(obj, key)
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Returns true if the given object has an enumerable, non-inherited property
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called `key`. [For information on enumerability and ownership of properties, see
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the MDN
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documentation.](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties)
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### forEachKey(obj, callback)
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Like Array.forEach, but iterates enumerable, owned properties of an object
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rather than elements of an array. Equivalent to:
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for (var key in obj) {
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if (Object.prototype.hasOwnProperty.call(obj, key)) {
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callback(key, obj[key]);
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}
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}
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### flattenObject(obj, depth)
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Flattens an object up to a given level of nesting, returning an array of arrays
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of length "depth + 1", where the first "depth" elements correspond to flattened
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columns and the last element contains the remaining object . For example:
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flattenObject({
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'I': {
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'A': {
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'i': {
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'datum1': [ 1, 2 ],
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'datum2': [ 3, 4 ]
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},
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'ii': {
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'datum1': [ 3, 4 ]
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}
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},
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'B': {
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'i': {
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'datum1': [ 5, 6 ]
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},
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'ii': {
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'datum1': [ 7, 8 ],
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'datum2': [ 3, 4 ],
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},
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'iii': {
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}
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}
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},
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'II': {
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'A': {
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'i': {
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'datum1': [ 1, 2 ],
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'datum2': [ 3, 4 ]
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}
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}
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}
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}, 3)
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becomes:
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[
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[ 'I', 'A', 'i', { 'datum1': [ 1, 2 ], 'datum2': [ 3, 4 ] } ],
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[ 'I', 'A', 'ii', { 'datum1': [ 3, 4 ] } ],
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[ 'I', 'B', 'i', { 'datum1': [ 5, 6 ] } ],
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[ 'I', 'B', 'ii', { 'datum1': [ 7, 8 ], 'datum2': [ 3, 4 ] } ],
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[ 'I', 'B', 'iii', {} ],
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[ 'II', 'A', 'i', { 'datum1': [ 1, 2 ], 'datum2': [ 3, 4 ] } ]
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]
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This function is strict: "depth" must be a non-negative integer and "obj" must
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be a non-null object with at least "depth" levels of nesting under all keys.
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### flattenIter(obj, depth, func)
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This is similar to `flattenObject` except that instead of returning an array,
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this function invokes `func(entry)` for each `entry` in the array that
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`flattenObject` would return. `flattenIter(obj, depth, func)` is logically
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equivalent to `flattenObject(obj, depth).forEach(func)`. Importantly, this
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version never constructs the full array. Its memory usage is O(depth) rather
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than O(n) (where `n` is the number of flattened elements).
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There's another difference between `flattenObject` and `flattenIter` that's
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related to the special case where `depth === 0`. In this case, `flattenObject`
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omits the array wrapping `obj` (which is regrettable).
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### pluck(obj, key)
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Fetch nested property "key" from object "obj", traversing objects as needed.
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For example, `pluck(obj, "foo.bar.baz")` is roughly equivalent to
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`obj.foo.bar.baz`, except that:
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1. If traversal fails, the resulting value is undefined, and no error is
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thrown. For example, `pluck({}, "foo.bar")` is just undefined.
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2. If "obj" has property "key" directly (without traversing), the
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corresponding property is returned. For example,
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`pluck({ 'foo.bar': 1 }, 'foo.bar')` is 1, not undefined. This is also
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true recursively, so `pluck({ 'a': { 'foo.bar': 1 } }, 'a.foo.bar')` is
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also 1, not undefined.
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### randElt(array)
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Returns an element from "array" selected uniformly at random. If "array" is
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empty, throws an Error.
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### startsWith(str, prefix)
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Returns true if the given string starts with the given prefix and false
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otherwise.
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### endsWith(str, suffix)
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Returns true if the given string ends with the given suffix and false
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otherwise.
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### parseInteger(str, options)
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Parses the contents of `str` (a string) as an integer. On success, the integer
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value is returned (as a number). On failure, an error is **returned** describing
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why parsing failed.
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By default, leading and trailing whitespace characters are not allowed, nor are
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trailing characters that are not part of the numeric representation. This
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behaviour can be toggled by using the options below. The empty string (`''`) is
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not considered valid input. If the return value cannot be precisely represented
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as a number (i.e., is smaller than `Number.MIN_SAFE_INTEGER` or larger than
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`Number.MAX_SAFE_INTEGER`), an error is returned. Additionally, the string
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`'-0'` will be parsed as the integer `0`, instead of as the IEEE floating point
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value `-0`.
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This function accepts both upper and lowercase characters for digits, similar to
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`parseInt()`, `Number()`, and [strtol(3C)](https://illumos.org/man/3C/strtol).
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The following may be specified in `options`:
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Option | Type | Default | Meaning
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------------------ | ------- | ------- | ---------------------------
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base | number | 10 | numeric base (radix) to use, in the range 2 to 36
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allowSign | boolean | true | whether to interpret any leading `+` (positive) and `-` (negative) characters
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allowImprecise | boolean | false | whether to accept values that may have lost precision (past `MAX_SAFE_INTEGER` or below `MIN_SAFE_INTEGER`)
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allowPrefix | boolean | false | whether to interpret the prefixes `0b` (base 2), `0o` (base 8), `0t` (base 10), or `0x` (base 16)
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allowTrailing | boolean | false | whether to ignore trailing characters
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trimWhitespace | boolean | false | whether to trim any leading or trailing whitespace/line terminators
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leadingZeroIsOctal | boolean | false | whether a leading zero indicates octal
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Note that if `base` is unspecified, and `allowPrefix` or `leadingZeroIsOctal`
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are, then the leading characters can change the default base from 10. If `base`
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is explicitly specified and `allowPrefix` is true, then the prefix will only be
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accepted if it matches the specified base. `base` and `leadingZeroIsOctal`
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cannot be used together.
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**Context:** It's tricky to parse integers with JavaScript's built-in facilities
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for several reasons:
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- `parseInt()` and `Number()` by default allow the base to be specified in the
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input string by a prefix (e.g., `0x` for hex).
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- `parseInt()` allows trailing nonnumeric characters.
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- `Number(str)` returns 0 when `str` is the empty string (`''`).
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- Both functions return incorrect values when the input string represents a
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valid integer outside the range of integers that can be represented precisely.
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Specifically, `parseInt('9007199254740993')` returns 9007199254740992.
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- Both functions always accept `-` and `+` signs before the digit.
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- Some older JavaScript engines always interpret a leading 0 as indicating
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octal, which can be surprising when parsing input from users who expect a
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leading zero to be insignificant.
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While each of these may be desirable in some contexts, there are also times when
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none of them are wanted. `parseInteger()` grants greater control over what
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input's permissible.
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### iso8601(date)
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Converts a Date object to an ISO8601 date string of the form
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"YYYY-MM-DDTHH:MM:SS.sssZ". This format is not customizable.
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### parseDateTime(str)
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Parses a date expressed as a string, as either a number of milliseconds since
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the epoch or any string format that Date accepts, giving preference to the
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former where these two sets overlap (e.g., strings containing small numbers).
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### hrtimeDiff(timeA, timeB)
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Given two hrtime readings (as from Node's `process.hrtime()`), where timeA is
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later than timeB, compute the difference and return that as an hrtime. It is
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illegal to invoke this for a pair of times where timeB is newer than timeA.
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### hrtimeAdd(timeA, timeB)
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Add two hrtime intervals (as from Node's `process.hrtime()`), returning a new
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hrtime interval array. This function does not modify either input argument.
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### hrtimeAccum(timeA, timeB)
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Add two hrtime intervals (as from Node's `process.hrtime()`), storing the
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result in `timeA`. This function overwrites (and returns) the first argument
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passed in.
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### hrtimeNanosec(timeA), hrtimeMicrosec(timeA), hrtimeMillisec(timeA)
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This suite of functions converts a hrtime interval (as from Node's
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`process.hrtime()`) into a scalar number of nanoseconds, microseconds or
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milliseconds. Results are truncated, as with `Math.floor()`.
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### validateJsonObject(schema, object)
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Uses JSON validation (via JSV) to validate the given object against the given
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schema. On success, returns null. On failure, *returns* (does not throw) a
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useful Error object.
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### extraProperties(object, allowed)
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Check an object for unexpected properties. Accepts the object to check, and an
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array of allowed property name strings. If extra properties are detected, an
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array of extra property names is returned. If no properties other than those
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in the allowed list are present on the object, the returned array will be of
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zero length.
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### mergeObjects(provided, overrides, defaults)
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Merge properties from objects "provided", "overrides", and "defaults". The
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intended use case is for functions that accept named arguments in an "args"
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object, but want to provide some default values and override other values. In
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that case, "provided" is what the caller specified, "overrides" are what the
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function wants to override, and "defaults" contains default values.
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The function starts with the values in "defaults", overrides them with the
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values in "provided", and then overrides those with the values in "overrides".
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For convenience, any of these objects may be falsey, in which case they will be
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ignored. The input objects are never modified, but properties in the returned
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object are not deep-copied.
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For example:
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mergeObjects(undefined, { 'objectMode': true }, { 'highWaterMark': 0 })
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returns:
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{ 'objectMode': true, 'highWaterMark': 0 }
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For another example:
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mergeObjects(
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{ 'highWaterMark': 16, 'objectMode': 7 }, /* from caller */
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{ 'objectMode': true }, /* overrides */
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{ 'highWaterMark': 0 }); /* default */
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returns:
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{ 'objectMode': true, 'highWaterMark': 16 }
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# Contributing
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See separate [contribution guidelines](CONTRIBUTING.md).
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