Array.prototype.join()
The join()
method creates and
returns a new string by concatenating all of the elements in an array
(or an array-like object),
separated by commas or a specified separator string. If the array has
only one item, then that item will be returned without using the separator.
Syntax
join()
join(separator)
Parameters
separator
Optional-
Specifies a string to separate each pair of adjacent elements of the array. The separator is converted to a string if necessary. If omitted, the array elements are separated with a comma (","). If
separator
is an empty string, all elements are joined without any characters in between them.
Return value
A string with all array elements joined. If arr.length
is
0
, the empty string is returned.
Description
The string conversions of all array elements are joined into one string.
Warning: If an element is undefined
, null
or an empty array
[]
, it is converted to an empty string.
Examples
Joining an array four different ways
The following example creates an array, a
, with three elements, then joins
the array four times: using the default separator, then a comma and a space, then a plus
and an empty string.
const a = ['Wind', 'Water', 'Fire'];
a.join(); // 'Wind,Water,Fire'
a.join(', '); // 'Wind, Water, Fire'
a.join(' + '); // 'Wind + Water + Fire'
a.join(''); // 'WindWaterFire'
Joining an array-like object
The following example joins array-like object
(arguments
),
by calling Function.prototype.call
on Array.prototype.join
.
function f(a, b, c) {
const s = Array.prototype.join.call(arguments);
console.log(s); // '1,a,true'
}
f(1, 'a', true);
//expected output: "1,a,true"
Specifications
Specification |
---|
ECMAScript Language Specification # sec-array.prototype.join |
Browser compatibility
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