如何使用 call 或 apply 调用 javascript 构造函数? [英] How can I call a javascript constructor using call or apply?
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问题描述
我如何概括下面的函数以接受 N 个参数?(使用电话还是申请?)
How could I generalise the function below to take N arguments? (Using call or apply?)
是否有一种编程方式可以将参数应用于new"?我不希望构造函数被视为普通函数.
Is there a programmatic way to apply arguments to 'new'? I don't want the constructor to be treated like a plain function.
/**
* This higher level function takes a constructor and arguments
* and returns a function, which when called will return the
* lazily constructed value.
*
* All the arguments, except the first are pased to the constructor.
*
* @param {Function} constructor
*/
function conthunktor(Constructor) {
var args = Array.prototype.slice.call(arguments, 1);
return function() {
console.log(args);
if (args.length === 0) {
return new Constructor();
}
if (args.length === 1) {
return new Constructor(args[0]);
}
if (args.length === 2) {
return new Constructor(args[0], args[1]);
}
if (args.length === 3) {
return new Constructor(args[0], args[1], args[2]);
}
throw("too many arguments");
}
}
qUnit 测试:
test("conthunktorTest", function() {
function MyConstructor(arg0, arg1) {
this.arg0 = arg0;
this.arg1 = arg1;
}
MyConstructor.prototype.toString = function() {
return this.arg0 + " " + this.arg1;
}
var thunk = conthunktor(MyConstructor, "hello", "world");
var my_object = thunk();
deepEqual(my_object.toString(), "hello world");
});
推荐答案
试试这个:
function conthunktor(Constructor) {
var args = Array.prototype.slice.call(arguments, 1);
return function() {
var Temp = function(){}, // temporary constructor
inst, ret; // other vars
// Give the Temp constructor the Constructor's prototype
Temp.prototype = Constructor.prototype;
// Create a new instance
inst = new Temp;
// Call the original Constructor with the temp
// instance as its context (i.e. its 'this' value)
ret = Constructor.apply(inst, args);
// If an object has been returned then return it otherwise
// return the original instance.
// (consistent with behaviour of the new operator)
return Object(ret) === ret ? ret : inst;
}
}
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