我需要创建一个 function 获取未知数量的参数并返回它们的乘法。 但是我得到的结果是不确定的

Question

I created an object and put the function in it, then used the bind method to give the function some parameters, but it is undefined in the console.

let numObj = {
    multyAll(...args) {
        for (let i = 0; i < args.length; i++) {
            if (typeof args === Number) {
                arguments *= arguments[i]
                return arguments
            }
        }
    }
    }

const result = numObj.multyAll.bind(1, 2, 3)
console.log(result());

I tried another way around but still, I don't know why I think the function ignores for loop and returns the value of mul which I gave in the beginning

let numObj = {
multyAll(...args) {
    let mul = 1
    for (arg of args) {
        if (typeof arg === Number) {
            mul *= arg
        }
        return mul
    }
    console.log(mul);
}
}

const result = numObj.multyAll.bind(1, 2, 3)
console.log(result());

Answer 1

Some issues:

• In the first version you use arguments which is a variable that gets automatically initialised with the function arguments. So to then use it for your product is not going to go well. The second version solves this point by using a different variable mul , which is properly initialised to 1.

• In the first version, typeof args is testing the wrong variable. It is not args you want to get the type of, but of args[i] . In the second version this is problem is solved.

• The typeof operator always returns a string, like "string", "number", "boolean", ... So that will never be equal to Number , which is a native function object, not a string.

• The return should not be inside the loop, as that will immediately stop the loop. You'll want to visit all arguments before returning, so that return must occur after the loop.

• bind takes as first argument the value that should serve as this during the function call. The other arguments will be the normal arguments that will be passed on during the call. So you need to insert an extra argument in the first spot, like null .

• You should scope your variables and not have them implicitly defined as globals. This is the case with arg in the second version. Insert a let or const there.

• Although the JavaScript engine will insert semicolons for you automatically, the rules for this can sometimes be tricky. It is better practice to take control over this yourself and separate your statements with semicolons.

Here is your second version (which was the better one) with the mentioned corrections:

 const numObj = { multyAll(...args) { let mul = 1; for (const arg of args) { if (typeof arg === "number") { mul *= arg; } } return mul; } }; const result = numObj.multyAll.bind(null, 1, 2, 3); console.log(result());

Finally, this task is well suited for solving with reduce :

 const numObj = { multyAll(...args) { return args.reduce((mul, arg) => mul * (typeof arg === "number"? arg: 1), 1 ); } }; const result = numObj.multyAll.bind(null, 1, 2, 3); console.log(result());