![]() In particular, every(), find(), findIndex(), findLast(), findLastIndex(), and some() do not always invoke callbackFn on every element - they stop iteration as soon as the return value is determined. The thisArg argument is irrelevant for any callbackFn defined with an arrow function, as arrow functions don't have their own this binding.Īll iterative methods are copying and generic, although they behave differently with empty slots. The this value ultimately observable by callbackFn is determined according to the usual rules: if callbackFn is non-strict, primitive this values are wrapped into objects, and undefined/ null is substituted with globalThis. The thisArg argument (defaults to undefined) will be used as the this value when calling callbackFn. ![]() What callbackFn is expected to return depends on the array method that was called. The array that the method was called upon. The index of the current element being processed in the array. The current element being processed in the array. Where callbackFn takes three arguments: element The following table lists the methods that mutate the original array, and the corresponding non-mutating alternative: Mutating methodĪn easy way to change a mutating method into a non-mutating alternative is to use the spread syntax or slice() to create a copy first: The following methods always create new arrays with the Array base constructor: splice() (to construct the array of removed elements that's returned).The following methods create new arrays by accessing nstructor to determine the constructor to use: Other methods mutate the array that the method was called on, in which case their return value differs depending on the method: sometimes a reference to the same array, sometimes the length of the new array. Primitive types such as strings, numbers and booleans (not String, Number, and Boolean objects): their values are copied into the new array.That is, if a referenced object is modified, the changes are visible to both the new and original arrays. Both the original and new array refer to the same object. Objects: the object reference is copied into the new array.Elements of the original array(s) are copied into the new array as follows: The copy always happens shallowly - the method never copies anything beyond the initially created array. They do so by first constructing a new array and then populating it with elements. Some methods do not mutate the existing array that the method was called on, but instead return a new array. Object.prototype._lookupSetter_() Deprecated.Object.prototype._lookupGetter_() Deprecated.Object.prototype._defineSetter_() Deprecated.If you do not specify any elements, splice() will only remove elements from the array. The elements to add to the array, beginning from start. In this case, you should specify at least one new element (see below). If deleteCount is 0 or negative, no elements are removed. However, if you wish to pass any itemN parameter, you should pass Infinity as deleteCount to delete all elements after start, because an explicit undefined gets converted to 0. ![]() If deleteCount is omitted, or if its value is greater than or equal to the number of elements after the position specified by start, then all the elements from start to the end of the array will be deleted. This is different from passing undefined, which is converted to 0.Īn integer indicating the number of elements in the array to remove from start. If start is omitted (and splice() is called with no arguments), nothing is deleted.Negative index counts back from the end of the array - if start = array.length, no element will be deleted, but the method will behave as an adding function, adding as many elements as provided.Zero-based index at which to start changing the array, converted to an integer. ![]()
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