js这段利用apply合并数组的代码没看懂

Question

求大佬详细说下下面代码的运行机制。

（这让我想到了好像以前就是利用apply来实现es6里面的...运算符？）

// `b` onto `a`:

a.push.apply( a, b );

a; // [1,2,3,4,5,6,7,8,9,"foo","bar","baz","bam","bun","fun"]

// or `a` into `b`:

b.unshift.apply( b, a );

b; // [1,2,3,4,5,6,7,8,9,"foo","bar","baz","bam","bun","fun"]

Answer 1

首先你要知道apply是干啥的，apply会改变方法的this指向为第一个参数，第二个参数是个数组