When I tried using Array.prototype.join on a multidimensional array, I encountered a surprising result. To investigate further, I looked into the inner workings of Array.prototype.join and found it to be native code.
[1,2,3,4,5,6,7,8].join('')
[1, [2], [3, [4, [5]]], [6, [7, [8]]]].join('');
I was expecting the output of
[1,[2],[3,[4,[5]]],[6,[7,[8]]]].join('')
to be
12345678
however, the actual output turned out to be
123,4,56,7,8
.join method utilizes .toString() function on every element to convert it into a string, while the default behavior of Array.prototype.toString() is to combine all elements using a comma ,.
console.log([1, 2, 3].toString());As mentioned by others, the toString function is invoked on the array. However, if you specify a separator, it will only join the array you are calling the method on with that particular separator.
[
1,
[2],
[3, [4, [5]]],
[6, [7, [8]]]
].join("")
This code snippet will concatenate the elements of the first level together, converting non-string elements to strings using the toString method.
1.toString() + "" +
[2].toString() + "" +
[3, [4, [5]]].toString() + "" +
[6, [7, [8]]].toString()
The empty string "" serves as the separator. The result will be 123,4,56,7,8, where 3,4,5 represents the first nested array and 6,7,8 corresponds to the second nested array (which contains more than one element). If you want to join the elements recursively, you can define your own custom method.
Array.prototype.deepJoin = function (separator) {
return this
.map(e => Array.isArray(e) ? e.deepJoin(separator) : e)
.join(separator);
};
var array = [1, [2], [3, [4, [5]]], [6, [7, [8]]]];
console.log(array.join());
console.log(array.deepJoin());
console.log(array.join(""));
console.log(array.deepJoin(""));
console.log(array.join(" - "));
console.log(array.deepJoin(" - "));The join method triggers the toString() function on each element.
Examples:
[2].toString() -> 2
[3, [4, 5]].toString() -> 3,4,5
It's important to note that the toString function for an array always removes square brackets.
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