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How to extract number from backwards in javascript in optimised way [closed]

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I have to extract a string from backwards upto 10 digits.
Use case is when we select a mobile number it is prefixed with country code sometimes and sometimes we get only the mobile number.
Let's say the number is : +91-84040355236545
I have to extract the number from the end say from 5 to last 10 degits so the end result would be 0355236545
I have a solution of using string.substring method

Here's a simple solution using substrings:
var number = "+91-84040355236545";
var lastTenDigitsNumber = number.substr(number.length - 10);
console.log(lastTenDigitsNumber);
A simpler solution is using slice:
var number = "+91-84040355236545";
console.log(number.slice(-10));
Another solution using a function and RegEX:
function extractTenDigits(number) {
var rx = /(\d{10}$)/g;
var arr = rx.exec(number);
return arr[1];
}
var number = "+91-84040355236545";
console.log(extractTenDigits(number));
I did a simple benchmark and the best solution for small quantity of numbers is the one using slice.
If you provide more details I can provide a more tailored suggestion.

You can try the following using substring :
let str = "+91-84040355236545";
str.substr(str.length - 10 ,10);

While loop and Strings [closed]

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Var randomLetters = "ljhgfdza";
Var randomString = "";
Now I'll have to add elements in the first variable to the second Randomly
Using the while loop, and Math.floor(Math.random() * random letters.length)
I am having a problem at my
"While (condition)" what should it be?

To flat out answer your question, you can use:
while(randomLetters.length > 0){
Then when you use a letter from randomLetters, you delete the letter and the length is now 1 less.

This will be enough for you:
const randomLetters = "ljhgfdza";
const returnRandom = (randomString) => {
const arrString = [...randomString].sort((a, b) =>{
return 0.5 - Math.random()
}).join("");
console.log(typeof arrString,arrString);
}
returnRandom(randomLetters);
but... in this case sort method is not that random as you think. This link will tell you why. I would do this with reduce() or map(), both are described in link above.

Javascript - Show all telephone numbers in a range [closed]

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If I have phone number ranges such as 5555555555-5599 5555550000-0003 5555550005-0007, my mission is to have it return all results without using a server. Is it possible for it to return without a server a result that would look like:
5555555555
5555555556
5555555557
/* etc */
My previous post about javascript has helped me up to this point but I wanted to rehaul the whole site.
Javascript dashes in phone number
If you could point me in the right direction, I would really appreciate it. I'm just having a mind block right now if this is even possible.

Given a single phone range in the form of "xxxxxxyyyy-zzzz", split the whole string on the dash and the first part of the string at the 6th index. This yields three strings "xxxxxx", "yyyy", and "zzzz". Using a for loop, you can create an array of phone numbers by concatenating the prefix "xxxxxx" onto the range "yyyy"-"zzzz":
// Get an array from a given range "xxxxxxyyyy-zzzz"
function fromRange(range) {
var phoneNumArray = [];
var prefix = range.substring(0,5);
var suffixRange = range.split("-");
for (var suffix = suffixRange[0].substring(4, -1);suffix < suffixRange[1];suffix++) {
phoneNumArray.push(prefix + suffix);
}
return phoneNumArray;
}
Try it in JSFiddle.

Javascript multipying without using * sign [closed]

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Practice Problem 1
Parameters: The function accepts two positive integers N and M.
Return Value: The function returns the product of N and M. For example, if the integers 5 and 8 are supplied to
that function, it should return the product of 5 and 8—it should return 40.
Additional
Requirements:
Do this without using the multiplication operator (*). Hint: Multiplication is just a series of addition
operations.

function mult(N, M) {
return N / (1 / M);
}

Since this is a basic excercise, I think that this answer is not expected (but maybe you'll get bonus points if you can explain it), even though it does the math without *.
function mult(N,M){
var a = new Array(N);
return a.join(""+M).split("").reduce((x,y)=>(parseInt(x)+parseInt(y)))+M
}
Note: This does not work for N < 3. No time to correct it.

OK. Look. It sounds like you're quite young so I think giving you the benefit of the doubt is alright here. So you know for the future: Stackoverflow isn't a site that you can just drop a homework question and expect people to do the work for you.
We sometimes do help with homework questions but only if it looks like you've at least attempted to answer the question yourself, by showing us some code that you've written. If you want to use SO in the future you might find the help section useful, particularly the section on how to write a good question.
OK, lecture over.
What the question is asking about is how to use a simple for loop to add some numbers together:
function getProduct(num1, num2) {
// set total to zero
// we'll be adding to this number in the loop
var total = 0;
// i is the index, l is the number of times we
// iterate over the loop, in this case 8 (num2)
for (var i = 0, l = num2; i < l; i++) {
// for each loop iteration, add 5 to the total
total += num1;
}
// finally return the total
return total;
}
getProduct(5, 8); // 40

Using a while loop to print random numbers until a certain number is reached [closed]

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How to use a while loop to generate random numbers until a certain number is reached? Help please

This code will generate integer numbers from 1 until 50.
var number = 50;
var x = 0;
while(x !== number){
x = Math.floor((Math.random() * 50) + 1);
console.log(x);
}

Considering there is a random number generator random you will just do as shown below
do
{
x=Math.random();
x=x*range;
if(x is desired number )
break;
else
{
print the number.
}
}while(1)
print -( desired number found).
NOTE: As you are beginner you can try the following when designing these codes..
First find what is the input and what is the output.
Then try to draw a flow chart of the whole thing ( You can try running it yourself as if you are the computer)
Then all the branch and loop are converted to if-else or for-while loop.
Check the code and match input and output.
This is a basic program structure..Instead of asking in forums about common structures try reading some books.
Hint 1: There is a function in javascript called Math.random() return a random number between 0 (inclusive) and 1 (exclusive):
Hint 2: check whether the values are equal. Use === in javascript.
Hint 3: check for if else, break and do while, while loop.
Hint 4: If you are given a random number 0<=x<1 then how do you generate a random number using in range [a,b) using the abobe geerated number? Ans: Use b*x.
hope this helps.