The entries()
method of Array instances returns a new array iterator object that contains the key/value pairs for each index in the array.
Syntax
entries()
Parameters
None.
Return value
A new iterable iterator object.
Description
When used on sparse arrays, the entries()
method iterates empty slots as if they have the value undefined
.
The entries()
method is generic. It only expects the this
value to have a length
property and integer-keyed properties.
Examples
Iterating with index and element
const a = ["a", "b", "c"];
for (const [index, element] of a.entries()) {
console.log(index, element);
}
// 0 'a'
// 1 'b'
// 2 'c'
Using a for...of loop
const array = ["a", "b", "c"];
const arrayEntries = array.entries();
for (const element of arrayEntries) {
console.log(element);
}
// [0, 'a']
// [1, 'b']
// [2, 'c']
Iterating sparse arrays
entries()
will visit empty slots as if they are undefined
.
for (const element of [, "a"].entries()) {
console.log(element);
}
// [0, undefined]
// [1, 'a']
Calling entries() on non-array objects
The entries()
method reads the length
property of this
and then accesses each property whose key is a nonnegative integer less than length
.
const arrayLike = {
length: 3,
0: "a",
1: "b",
2: "c",
3: "d", // ignored by entries() since length is 3
};
for (const entry of Array.prototype.entries.call(arrayLike)) {
console.log(entry);
}
// [ 0, 'a' ]
// [ 1, 'b' ]
// [ 2, 'c' ]