Enhancement: expose isIndex, isLength and complimentary toLength

[Xotic750]

Change reIsUint to pick up number string literals beginning with 0.
Change isLength, add length argument, use other lodash methods
Add toLength as it doesn't exist.
These are all useful methods that I find myself using and lodash mostly has them internally.

var MAX_SAFE_INTEGER = Number.MAX_SAFE_INTEGER || Math.pow(2, 53) - 1;

/** Used to detect unsigned integer values. */
var reIsUint = /^(\d|[1-9]\d+)$/;

/**
 * Checks if `value` is a valid array-like index.
 *
 * @param {*} value The value to check.
 * @param {number} [length=MAX_SAFE_INTEGER] The upper bounds of a valid index.
 * @returns {boolean} Returns `true` if `value` is a valid index, else `false`.
 */
function isIndex(value, length) {
  value = (typeof value == 'number' || reIsUint.test(value)) ? +value : -1;
  length = length == null ? MAX_SAFE_INTEGER : length;
  return value > -1 && value % 1 == 0 && value < length;
}

/**
 * Checks if `value` is a valid array-like length.
 *
 * **Note:** This function is based on [`ToLength`](http://ecma-international.org/ecma-262/6.0/#sec-tolength).
 *
 * @param {*} value The value to check.
 * @param {number} [length=MAX_SAFE_INTEGER] The upper bounds of a valid length.
 * @returns {boolean} Returns `true` if `value` is a valid length, else `false`.
 */
function isLength(value, length) {
  value = (typeof value == 'number' || reIsUint.test(value)) ? +value : -1;
  length = length == null ? MAX_SAFE_INTEGER : length;
  return value > -1 && value % 1 == 0 && value <= length;
}

/**
 * The abstract operation ToLength converts its argument to an integer
 * suitable for use as the length of an array-like object.
 *
 * **Note:** This function is based on [`ToLength`](http://ecma-international.org/ecma-262/6.0/#sec-tolength).
 *
 * @param {*} value The object to be converted to a length.
 * @param {number} [length=MAX_SAFE_INTEGER] The upper bounds of a valid length.
 * @return {number} If len <= 0 then 0 else if len is +INFINITY then 2^53-1
 *                  else min(len, 2^53-1).
 */
function toLength(value, length) {
  length = length == null ? MAX_SAFE_INTEGER : length;
  return _.clamp(_.toInteger(value), 0, length);
}

[jdalton]

I want to hold off on exposing isIndex and isLength because I don't think they're useful outside of internals opting for using _.isArrayLike instead. Do you have a use case in mind?

[Xotic750]

One example (isIndex) is when patching buggy defineProperty/defineProperties, I've also used it for a hasProperty method, where native in isn't enough (buggy). Possibly I could do the same with _.isArrayLike, but would need to check. isLength I've used several times, again _.isArrayLike may work instead. So these would just be nice to haves I guess. toLength I use frequently, for all sorts of methods where I want the interface to have an ES feel about it. So this I would definitely like out of all of them. Pretty much every occasion where you may consider value >>> 0, but toLength is much nicer I think. You still may want to consider a regex change though, even internally.

[jdalton]

Pretty much every occasion where you may consider value >>> 0, but toLength is much nicer I think

Ah good point. I'll accept a PR for exposing isLength and adding a toLength.

You still may want to consider a regex change though, even internally.

I want to keep isIndex internal but hardening the reIsUint to avoid letting '0001' slip through is a good idea so I'll accept a different PR for that too.

[Xotic750]

Sounds reasonable. Now, the question is can I work git to have multiple branches for concurrent PRs. I've only worked with having a master and that is occupied with the toNumber PR. Or maybe I'll just wait a bit. :)

[jdalton]

You can create a branch as:

cd lodash
git checkout master
git branch isLength
git checkout isLength
# do stuff
git push origin isLength
git checkout master
git branch reIsUnit
git checkout reIsUnit
# do stuff
git push origin reIsUnit
git checkout master

[Xotic750]

I'll give it a try and hopefully not end up in too much of a mess.

[Xotic750]

I'm assuming that you want isLength to remain as is and just be exposed (if I am understanding correctly), as my suggested change would cause a difference in results. As currently it must specifically be of type number rather than something that coerces to a valid number of isLength?

[jdalton]

Exposed methods get a bit more robust to handle more edge cases. To start out the PR could just expose them as is and I'll comment tweak once the PR is opened.

[Xotic750]

Ok, I will give that a try and see how it goes with git. :)

[lock]

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