JavaScript Arrays Concatenating Arrays
Example
Two Arrays
var array1 = [1, 2];
var array2 = [3, 4, 5];
3
var array3 = array1.concat(array2); // returns a new array
6
var array3 = [...array1, ...array2]
Results in a new Array:
[1, 2, 3, 4, 5]
Multiple Arrays
var array1 = ["a", "b"],
array2 = ["c", "d"],
array3 = ["e", "f"],
array4 = ["g", "h"];
3
Provide more Array arguments to array.concat()
var arrConc = array1.concat(array2, array3, array4);
6
Provide more arguments to []
var arrConc = [...array1, ...array2, ...array3, ...array4]
Results in a new Array:
["a", "b", "c", "d", "e", "f", "g", "h"]
Without Copying the First Array
var longArray = [1, 2, 3, 4, 5, 6, 7, 8],
shortArray = [9, 10];
3
Provide the elements of shortArray as parameters to push using Function.prototype.apply
longArray.push.apply(longArray, shortArray);
6
Use the spread operator to pass the elements of shortArray as separate arguments to push
longArray.push(...shortArray)
The value of longArray is now:
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
Note that if the second array is too long (>100,000 entries), you may get a stack overflow error (because of how apply works). To be safe, you can iterate instead:
shortArray.forEach(function (elem) {
longArray.push(elem);
});
Array and non-array values
var array = ["a", "b"];
3
var arrConc = array.concat("c", "d");
6
var arrConc = [...array, "c", "d"]
Results in a new Array:
["a", "b", "c", "d"]
You can also mix arrays with non-arrays
var arr1 = ["a","b"];
var arr2 = ["e", "f"];
var arrConc = arr1.concat("c", "d", arr2);
Results in a new Array:
["a", "b", "c", "d", "e", "f"]
