[INTERVIEW] Coding challenge to test scope, ES6, IIFE

cc_scope_iife.js

// Remember to overwite the code in CodeShare, JSFiddle, etc. to restore the inital state of the test and to avoid
// showing to candidates the changes made during other interwies

// TASKS:
// 1. Ask to developer to analyze the provide (broken) snippet:
//    - The dev should be able to understand the intent of the snipped
//    - The dev should be able to predict the (unexpected) behaviour
//    - The dev should be able to provide at least one fix (and discuss about it)

const initialValues = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
const summedValues = [];

// BROKEN VERSION: Uses "var", not scoped
for (var i = 0; i < initialValues.length; i++) {
    summedValues.push(() => {
      console.log(initialValues[i]);
    });
}

console.log(summedValues.forEach(v => v())) // 10x Undefined

// JUST REFERENCE, DELETE BEFORE INTERVIEWING
// CORRECT VERSION: Uses "let", at every iteration different instances of the variable i
for (let i = 0; i < initialValues.length; i++) {
    summedValues.push(() => {
      console.log(initialValues[i]);
    });
}

console.log(summedValues.forEach(v => v())) // 0, 1, 2, 3, 4, ...

// JUST REFERENCE, DELETE BEFORE INTERVIEWING
// CORRECT VERSION: Uses IIFE, i is scoped inside the IIFE
for (let i = 0; i < initialValues.length; i++) {
    summedValues.push((() => () => (console.log(initialValues[i])))());
}

console.log(summedValues.forEach(v => v())) // 0, 1, 2, 3, 4, ...

Links

CodeShare - JSFiddle