js 实现call
手写call
/**
* 实现call
* @param {*} context
* fn.call(target,...args)
* 让fn中的this指向target
* 思路是函数默认指向调用者,在目标对象上挂载fn,执行的时候fn中的this默认指向目标对象, 执行完拿到结果并删除这个挂载属性即可
*/
Function.prototype._call = function(context){
if(typeof this !== 'function'){
throw 'Error'
}
context = context || window
context.fn = this
const args = Array.from(arguments).slice(1)
const result = context.fn(...args)
delete context.fn
return result
}
const fn = function(){console.log(this); return {a:1,...this}}
fn._call({test:1})