Array (Queue, Stack, Tree)

1. forEach() and map()

What's the difference between forEach() and map()?

1. Return value
2. ?
3. ?

What does

const arr = [0, 0, 0, 0, 1, 0, 0, 0];
arr.forEach(function(val, index) {
    if (val === 1) break;
    else arr[index] = 3;
})
console.log(arr);        // ?

Answer is Uncaught SyntaxError: Illegal break statement. There's no built-in ability to break in forEach.

2. every() and some()

What's the difference between every() and some()?

3. slice() and splice()

There's no splice() for strings.

Array.prototype.slice;           // exist
String.prototype.slice;          // exist

Array.prototype.splice;          // exist
String.prototype.splice;         // undefined, use subString() or slice()

Use splice to insert items into array:

//

3. Implement Stack using Array

How to use array as stack?

const stack = [];    // stack: []
stack.pop()          // undefined
stack.push(1)        // stack: [1]
stack.push(3)        // stack: [1, 3]
stack.pop()          // stack: [1], 3 is returned
stack[stack.length-1];    // peak()

4. Implement Queue using Array

How to use array as queue?

const queue = [];    // queue: []
queue.push(2);       // queue: [2]        
queue.push(4);       // queue: [2, 4]
const i = queue.shift()    // queue: [4], 2 is returned

5. Sort Array

What will the following return?

[1,2,11,3].sort();

Answer is: [1, 11, 2, 3].

A little surprising right? Reason is sort(comparator)'s default comparator treats array items as string.

Fix:

[1, 2, 11, 3].sort((a, b) => a - b);
// [1, 2, 3, 11]

More about Array.prototype.sort(): https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort

References:

1. 9 JavaScript Tips You May Not Know http://codetunnel.io/9-javascript-tips-you-may-not-know/
2. Interviewing a front-end developer http://blog.sourcing.io/interview-questions?utm_source=ourjs.com
3. How to short circuit Array.forEach like calling break http://stackoverflow.com/questions/2641347/how-to-short-circuit-array-foreach-like-calling-break