题解 | #修改 this 指向#

call()、bind()、apply()的用法，改变this的指向，区别在于
f.call(obj, arg1, arg2...),
f.bind(obj, arg1, arg2,...)(),
f.apply(obj, [arg1, arg2, .])

1. apply

   function bindThis(f, oTarget) {
    return function() {
        return f.apply(oTarget, arguments)
    }
   }

2. bind

   function bindThis(f, oTarget) {
    return f.bind(oTarget)
   }

3. call

   function bindThis(f, oTarget) {
    return function() {
        return f.call(oTarget, ...arguments)
    }
   }