手写call，bind，apply

foo.Mycall(obj,1,2,3)
Function.prototype.Mycall=function(target,...args){if(typeof this!=='function'){throw new TypeError('this is not a function')}// 判断target是否是对象if(target==null||target==undefined){target=window}if(typeof target!=='object'){target=Object(target)}// 把this作为target的方法let key=new Symbol()target[key]=this;let res=target[key](...args)delete target[key]return res
}

apply和call差不多，都是直接返回函数执行的结果

区别：apply传入的参数是数组

foo.Myapply(obj,[1,2,3])Function.prototype.Myapply=function(target,args){if(typeof this!=='function'){throw new TypeError('this is not a function')} if(target==null||target===undefined){target=window}if(typeof target!=='object'){target=Object(target)}let key=new Symbol()target[key]=this;let res=target[key](...args)delete target[key]return res
}

bind:

Function.prototype.bind=function(context,...args){if(typeof this!=='function'){throw new Error('this is not a function')}if(context==null||context==undefined){context=window}if(context!=='object'){context=Object(context)}let key=new Symbol()context[key]=this;return function(...newargs){let res=context[key](...args,...newargs)delete context[key]return res}
}