在函数内部设置javascript参数

Question

How to set variable which I pass to a function

function checkSetName(inputVar, outputVar, txt){
            if (inputVar.length) {
                outputVar = txt + ': ' + inputVar.val();
            } else {
                outputVar = "";
            }
        }
checkSetName(name, nameTxt, 'Hello world ');

I pass the empty variable nameTxt and I expect it to be set the value inside of function, but after function executes the variable is undefined

How to set variable that I pass to a function in JavaScript

Answer 1

You can't because JS is a strictly pass-by-value language, there are no ByRef parameters. Just return a value.

function checkSetName(inputVar, txt){
        if (inputVar.length) {
            return txt + ': ' + inputVar.val();
        } else {
            return  = "";
        }

Another (worse) option is to pass an object and modify its state:

function checkSetName(inputVar, state, txt){
        if (inputVar.length) {
            state.output = txt + ': ' + inputVar.val();
        } else {
            state.output = "";
        }

Finally, you can make your a function a method and modify this instead of a parameter object:

class Validations {
    checkSetName(inputVar, txt){
        if (inputVar.length) {
            this.output = txt + ': ' + inputVar.val();
        } else {
            this.output = "";
        }
}