Javascript Techniques

Question 1

Convert a number into array in JavaScript

Answer 1

1. Array.from() Method
var myInt = 235345;

// Getting the string as a parameter
// and typecasting it into an integer
let myFunc = num => Number(num);

var intArr = Array.from(String(myInt), myFunc);

// Print the result array
console.log(intArr);

2. .map() Method
// Declare a variable and store an
// integer value
var num = 235345

// Here we typecasting the num
// Splitting the num, so that
// we got an array of strings
// Then use map function to
// convert the array of strings
// into array of numbers

var myArr = String(num).split("").map((num)=>{
  return Number(num)
})

console.log(myArr)

3. using .reduce() function
var myInt = 235345;

// number to string convertion
var temp = ''+myInt
// forming array with numbers as element
var intArr = [...temp].reduce((acc, n)=> acc.concat(+n), [ ] );

// Print the result array
console.log(intArr);

Question 2

Use a variable in a JS RegEx

Answer 2

The right way of doing it is by using a regular expression constructor new RegExp().

let pattern = “\d”;
let re = new RegExp(\\b${pattern}\\b, ‘gi’);
console.log(inputString.replace(re, “Google”));

const str = "Hello yes what are you yes doing yes"
const removeStr = "yes" //variable
const regex =  new RegExp(removeStr,'g'); // correct way
const newstr = str.replace(regex,''); // it works

In the above code, we have passed the removeStr variable as an argument to the new RegExp() constructor method.

Question 3

Clone an Array

Answer 3

1. Spread Operator (shallow copy):
   numbers = [1, 2, 3];
   numbersCopy = […numbers];
2. For Loop (shallow copy)
   numbers = [1, 2, 3];
   numbersCopy = [];

for (i = 0; i < numbers.length; i++) {
numbersCopy[i] = numbers[i];
}

3. While Loop (shallow copy)
   numbers = [1, 2, 3];
   numbersCopy = [];
   i = -1;

while (++i < numbers.length) {
numbersCopy[i] = numbers[i];

4. Array.map() (shallow copy)
   numbers = [1, 2, 3];
   double = (x) => x * 2;

numbers.map(double);

5. Cloning
   identity = (x) => x;
   numbers.map(identity);
   // [1, 2, 3]
6. Array Filter (shallow copy)
   numbers = [1, 2, 3];
   numbersCopy = numbers.filter(() => true);
7. Array.reduce (shallow copy)
   numbers = [1, 2, 3];

numbersCopy = numbers.reduce((newArray, element) => {
newArray.push(element);

return newArray;
}, []);

8. Array.slice (shallow copy)
   numbers = [1, 2, 3, 4, 5];
   numbersCopy = numbers.slice();
   // [1, 2, 3, 4, 5]
9. JSON Parse and Stringify (deep copy)
   nestedNumbers = [[1], [2]];
   numbersCopy = JSON.parse(JSON.stringify(nestedNumbers));

numbersCopy[0].push(300);
console.log(nestedNumbers, numbersCopy);

// [[1], [2]]
// [[1, 300], [2]]
// These two arrays are completely separate!

10. Array.concat (shallow copy)
    [1, 2, 3].concat(); // [1, 2, 3]
    [1, 2, 3].concat([]); // [1, 2, 3]
11. Array.from() (shallow copy)
    numbers = [1, 2, 3];
    numbersCopy = Array.from(numbers);
    // [1, 2, 3]