How to return a value from forEach [duplicate]

Question

I'm really new to JavaScript, and I've encountered a problem that I don't understand.

I wanted to write function which takes an array as an argument, and returns true if all elements in the array are identical.

By now I know that a simple for loop is more effective, but I wanted to do this simple function with forEach().

function isUniform(array) {
    let uniChecker = array[0];
    array.forEach(function(element) {
        if (uniChecker !== element) {
            return false;
        }
    });
    return true;
}

It always returns true, even if it should return false.

Answer 1

Unfortunately returning from the forEach callback does nothing to the outer scope, it simply exits the callback scope. While forEach can be used it's not the most efficient as there's no real way of exiting the loop early.

Better alternatives would be every / some, these functions are designed to test items in an array and detect anomalies (determined by whatever condition you provide) and exit on the first mismatch e.g.

const isUniform = arr => arr.every(x => arr[0] === x)

Playground

const arr = [1,1,3,1,1,2]
// using `every` (recommended)
console.log(`Using 'every'...`);
let isUniform = arr => arr.every(x => {
  console.log(`Testing ${x}`);
  return arr[0] === x;
});
console.log(isUniform(arr));
// using `some` (bit more complicated but can still work)
console.log(`Using 'some'...`);
isUniform = arr => !arr.some(x => {
  console.log(`Testing ${x}`);
  return arr[0] !== x;
});
console.log(isUniform(arr));

Answer 2

forEach() throws away return values and always returns undefined

so no matter what you do inside your code the return value from forEach is never returned

You can create a flag that sets to false when your condition is met(Its a suggestion if you want to go with ForEach)

function isUniform(array) {
 let flag=true;
    let uniChecker = array[0];
    array.forEach(function(element) {
        if (uniChecker !== element) {
          flag=false;
        }
    });
    return flag;
}