Production steps of ECMA-262, Edition 5, 15.4.4.18 // Reference: if ( ! Array. The typical use case is to execute side effects at the end of a chain.įorEach() does not mutate the array on which it is called (although callback, if invoked, may do so). using shift()) during the iteration, later elements will be skipped - see example below.įorEach() executes the callback function once for each array element unlike map() or reduce() it always returns the value undefined and is not chainable. If elements that are already visited are removed (e.g. If the values of existing elements of the array are changed, the value passed to callback will be the value at the time forEach() visits them elements that are deleted before being visited are not visited. Elements that are appended to the array after the call to forEach() begins will not be visited by callback. The range of elements processed by forEach() is set before the first invocation of callback. The this value ultimately observable by callback is determined according to the usual rules for determining the this seen by a function. Otherwise, the value undefined will be used as its this value. If a thisArg parameter is provided to forEach(), it will be used as callback's this value. on sparse arrays).Ĭallback is invoked with three arguments: It is not invoked for index properties that have been deleted or are uninitialized (i.e. () (en-US)įorEach() executes the provided callback once for each element present in the array in ascending order. Object.prototype._lookupSetter_() (en-US) 已棄用.Object.prototype._lookupGetter_() (en-US) 已棄用.Object.prototype._defineSetter_() (en-US) 已棄用.
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