如果 JavaScript 中的赋值为 false，则返回简写？

Question

In a JavaScript function I would like to return if a given value is null.

While this works:

const A = this.B;

if (!A) {
   return;
}

// More code...

I would like to know if there's a simpler form to do this:

These don't work:

const A = this.B || return;

// More code...

const A = this.B;
                                                                                   
!A || return;

// More code...

Is there a possible shorthand for this?

Answer 1

Unfortunately there is no such shorthand. return is a statement, not an expression, and the only way to evaluate statements conditionally is if . Operators (AND, OR, ternary and so on) can help you evaluate expressions, but not statements

Answer 2

Depending on actual code :

• if it just returns or should return a value
• on how many places
• what code is before (eg variables to be used further)
• what code is after
• etc. etc...

the following approach can be used.

Instead of if (!A) return; or (not working) !A || return; !A || return; , you return !A || theRestOfTheCodePutIntoAnotherFunction(); return !A || theRestOfTheCodePutIntoAnotherFunction();

An example of "original" code:

class Test {
    constructor(b) {
        this.b = b
    }
    test() {
        const a = this.b
        if (!a) {
            return
        }
        console.log("TEST")
    }
}
console.log("test 0")
new Test(0).test()
console.log("test 1")
new Test(1).test()

and modified version

class Test {
    constructor(b) {
        this.b = b
    }
    test() {
        const a = this.b
        return !a || this.test2()
    }
    test2() {
        console.log("TEST")
    }
}
console.log("test 0")
new Test(0).test()
console.log("test 1")
new Test(1).test()