How to create a function that will concatenate any given string with second parameter?

Question

I am trying to create a function that I can reuse with any string, passing a string as a first parameter and concatenating operator to it as I am trying to create a basic calculator and I am working with couple of strings which display different values for operators(e.g. 'x' instead of '*').

let evalString = '';
let displayString = '';
let currentNumber = '5';

function concOperator(str, operator) {
  str += currentNumber + ' ' + operator + ' ';
}

concOperator(evalString, '*');
concOperator(displayString, 'x');

console.log(evalString);
console.log(evalString);

So I expect the evalString to be "5 * " and displayString to be "5 x " after calling a function, but instead it returns empty strings. How could it be fixed?

Answer 1

It's because you're not returning anything in your function and you're not assigning it to your variable. Actually, str is in the scope of concOperator function.

A way to fix this:

let evalString = '';
let displayString = '';
let currentNumber = '5';

function concOperator(str, operator) {
    return `${str} ${currentNumber} ${operator} `;
}

evalString = concOperator(evalString, '*');
displayString = concOperator(displayString, 'x');