js method of merging arrays

Reference: Several ways to merge js arrays

1. Concat: Generate a new array without changing the original array

	var arr1 = [1, 2, 3];
	var arr2 = ['a', 'b', 'c'];
	var newArr = arr1.concat(arr2);
	console.log(newArr);// [1, 2, 3, "a", "b", "c"]
	console.log(arr1 );// [1, 2, 3] 

2. Loop traversal

	var arr1 = [1, 2, 3]
    var arr2 = ['a', 'b', 'c']
    for (var i = 0; i < arr2.length; i++) {
      arr1.push(arr2[i])
    }
    console.log(arr1);//[1, 2, 3, "a", "b", "c"]

3、apply

	var arr1 = [1, 2, 3]
    var arr2 = ['a', 'b', 'c']
	arr1.push.apply(arr1,arr2);
	//  Array.prototype.push.apply(arr1,arr2);
	console.log(arr1) //[1, 2, 3, "a", "b", "c"]

4. ES6 syntax: ... operator

	var arr1 = [1, 2, 3]
    var arr2 = ['a', 'b', 'c']
	var newArr = [...arr1, ...arr2]; //[1, 2, 3, "a", "b", "c"];