# js 中什么是 softbind，如何实现
Issue
欢迎在 Gtihub Issue 中回答此问题: Issue 33 (opens new window)
Author
bind 函数多次调用会已第一次绑定的 this 为准，softbind 已最后一次绑定传入的 this 为准；
Author
Function.prototype.softBind = function(obj, ...rest) {
const fn = this
const bound = function(...args) {
const o = !this || this === (window || global) ? obj : this
return fn.apply(o, [...rest, ...args])
}
bound.prototype = Object.create(fn.prototype)
return bound
}
function foo() {
console.log(name: ${this.name});
}
let obj = {name: "obj"};
obj2 = {name: "obj2"};
obj3 = {name: "obj3"};
let fooBJ = foo.softBind(obj);
fooBJ(); // name: obj 这个时候软绑定已经生效了，this绑定到obj上
obj2.foo = foo.softBind(obj);
obj2.foo(); //name: obj2 这里已经的this隐式绑定到obj2上了
fooBJ.call(obj3); // name: obj3 这里this被硬绑定到obj3上了
setTimeout(obj2.foo, 100); // name: obj 软绑定了最初的obj
Author
TODO
Author
bound.prototype = Object.create(fn.prototype); 为什么要有这一句，不是很懂
Author
Function.prototype.softBind = function (obj, ...args) {
const fn = this;
return function (...args2) {
return fn.apply(this === global ? obj : this, args.concat(args2));
};
};