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I read on Javascript: The Good Parts...
Since JavaScript’s arrays are really objects, the
for instatement can be used to iterate over all of the properties of an array. Unfortunately, for in makes no guarantee about the order of the properties...
As far as I know the "each" functions are based in for in, then does each function form JQuery and Underscore libraries guarantee order when they iterate over an Array? I'm trying to avoid the annoying standard for.
Thank you in advance.
576
Sorting an array of objects in javascript is simple enough using the default sort() function for all arrays: const arr = [ { name: "Nina" }, { name: "Andre" }, { name: "Graham" } ]; const sortedArr = arr.
forEach() does not mutate the array on which it is called. (However, callback may do so).
Differences between forEach() and map() methods:The forEach() method does not create a new array based on the given array. The map() method creates an entirely new array. The forEach() method returns “undefined“. The map() method returns the newly created array according to the provided callback function.
Iterating over an array You can iterate over an array using for loop or forEach loop. Using the for loop − Instead on printing element by element, you can iterate the index using for loop starting from 0 to length of the array (ArrayName. length) and access elements at each index.
When iterating through an array, order is always guaranteed. It's when you iterate through (non-array) objects is when there's no guarantee. Arrays are still objects by the way.
each is no more than a for in for objects, and for for array-like. the framework determines the right loop for the job and the same logic applies: Arrays iterations are orderly while object iteration isn't.
Underscore's source:
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 (i in obj && 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;
}
}
}
};
jQuery's source:
each: function (object, callback, args) {
var name, i = 0,
length = object.length,
isObj = length === undefined || jQuery.isFunction(object);
if (args) {
if (isObj) {
for (name in object) {
if (callback.apply(object[name], args) === false) {
break;
}
}
} else {
for (; i < length;) {
if (callback.apply(object[i++], args) === false) {
break;
}
}
}
// A special, fast, case for the most common use of each
} else {
if (isObj) {
for (name in object) {
if (callback.call(object[name], name, object[name]) === false) {
break;
}
}
} else {
for (; i < length;) {
if (callback.call(object[i], i, object[i++]) === false) {
break;
}
}
}
}
return object;
}
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