[Understand Underscore and Lo-Dash] Collections _. each

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• Aliases
• Arguments
• Returns
• Aliases
• Arguments
• Returns

_. Each

Traverses the set and calls back each element in the set.

APILo-Dash

_. ForEach (collection [, callback = identity, thisArg])

Aliases

Each

Arguments

1. collection (Array | Object | String): Set to be traversed
2. [callback=identity] (Function): Functions called in each iteration
3. [thisArg] (Arbitrary): BindcallbackOfthis
4. callbackThree parameters are accepted:(value, index|key, collection)

Returns

(Array, Object, String): Returncollection.

Underscore

_. Each (list, iterator, [context])

Aliases

ForEach

Arguments

1. list (Array | Object | String): Set to be traversed
2. iterator (Function): Functions called in each iteration
3. [context] (Arbitrary): BindcallbackOfthis
4. iteratorThree parameters are accepted:(element|value, index|key, list)

Returns

(Array, Object, String): Returnundefined.

Note

• Lo-Dash can omit the callback function, while Underscore must be passed in
• Lo-Dash can be returned through callbackfalseEnd iteration ahead of schedule
• Lo-Dash returns the Collection to allow chained operations. The returned value of Underscore is undefined.

ExampleLo-Dash

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_. ForEach ([1, 2]) // => Returns [1, 2, 3] _ ([1, 2, 3]). forEach (alert ). join (','); // => alert returns '1, 2, 3 '_ for each number '_. forEach ({'one': 1, 'two': 2, 'three ': 3}, alert ); // => alert each number value (not necessarily executed in the defined order)

Underscore

1234	_. Each ([1, 2, 3], alert); // => alert each number _. each ({one: 1, two: 2, three: 3}, alert); // => alert each number value (not necessarily in the defined order)

SourceLo-Dash

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function forEach(collection, callback, thisArg) { var index = -1, length = collection ? collection.length : 0; callback = callback && typeof thisArg == 'undefined' ? callback : lodash.createCallback(callback, thisArg); if (typeof length == 'number') { while (++index < length) { if (callback(collection[index], index, collection) === false) { break; } } } else { forOwn(collection, callback); } return collection;}

Underscore

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var each = _.each = _.forEach = function(obj, iterator, context) { if (obj == null) return; if (nativeForEach && obj.forEach === nativeForEach) { obj.forEach(iterator, context); } else if (obj.length === +obj.length) { for (var i = 0, l = obj.length; i < l; i++) { if (iterator.call(context, obj[i], i, obj) === breaker) return; } } else { for (var key in obj) { if (_.has(obj, key)) { if (iterator.call(context, obj[key], key, obj) === breaker) return; } } } };

Additional

• obj.length === +obj.length

+obj: Convert obj to a decimal number; otherwise, returnNaN. Therefore, the above judgment is equivalentobj.length && typeof obj.length == 'number'

• if (iterator.call(context, obj[i], i, obj) === breaker) return;

breakerIs a pre-defined empty object ({}). Underscore is used internally to end the cycle in advance and is not made public to the public. In addition, because the object's===The object address is compared, so even if the user returns{}ifStill not valid

• for inLoop does not traverse the non-enumerable attribute, so likeObjectOftoStringWill not be iterated