Wherever I run my javascript code it freezes my computer, why this happens please let me know?

Question

var y;
function deci(y) {
  var res = "";

  while (y != 1) {
    res = res + y % 2;
    y = y / 2;
  }

  return (1 + res);
}

Answer 1

What you could do

• change the loop to a do ... while loop, because it loops at least one time, for zero values,

• switch the assignment of res to res = y % 2 + res;, because it has the right order now,

• take the integer value of the divided value for the next loop,

• check the value and go on with non zero values.

function deci(y) {
    var res = "";
    do {
        res = y % 2 + res;
        y = Math.floor(y / 2);
    } while (y)
    return res;
}

console.log (deci(0));
console.log (deci(1));
console.log (deci(2));
console.log (deci(3));
console.log (deci(4));
console.log (deci(5));
console.log (deci(13));

Answer 2

This to me looks like an endless loop. Try to modify the condition to y >= 1

var y;
function deci(y) {
  var res = "";

  while (y >= 1) {
    res = res + y % 2;
    y = y / 2;
  }

  return (1 + res);
}

Answer 3

Three problems

• global y is bad practice – you're shadowing it with a local y so I'm guessing you didn't intend to do this
• Your while condition is broken – repeatedly dividing a number by 2 will not always reach 1
• JavaScript performs floating point division, so you need to truncate the decimal

This is probably what you meant to write

const deci = y =>
{
  let res = ''
  while (y >= 2)
  {
    res = res + String (y % 2)
    y = y / 2 >> 0
  }
  return res + String (y)
}
    
console.log (deci (0))
console.log (deci (1))
console.log (deci (2))
console.log (deci (3))
console.log (deci (4))
console.log (deci (5))

Here's another way you can write the program

const deci = y =>
  y < 2
    ? String (y)
    : deci (y / 2 >> 0) + String (y % 2)
    
console.log (deci (0))
console.log (deci (1))
console.log (deci (2))
console.log (deci (3))
console.log (deci (4))
console.log (deci (5))

A default parameter value and better name make this function a little nicer to read, imo

const decimalToBinary = (n = 0) =>
  n < 2
    ? String (n)
    : decimalToBinary (n / 2 >> 0) + String (n % 2)

As @NinaScholz points out, you can perform n / 2 >> 0 in a single operation n >> 1 - the function is further improved

const decimalToBinary = (n = 0) =>
  n < 2
    ? String (n)
    : decimalToBinary (n >> 1) + String (n % 2)

Alternatively, we could make 2 a parameter of our function to create a generic base converter

const decimalToBase = (n = 0, base = 2) =>
  n < base
    ? String (n)
    : decimalToBase (n / base >> 0) + String (n % base)
    
const decimalToBinary = (n = 0) =>
  decimalToBase (n, 2)
  
const decimalToOctal = (n = 0) =>
  decimalToBase (n, 8)
  
console.log (decimalToBinary (0), decimalToOctal (0)) // 0     0
console.log (decimalToBinary (1), decimalToOctal (1)) // 0     1
console.log (decimalToBinary (2), decimalToOctal (2)) // 10    2
console.log (decimalToBinary (7), decimalToOctal (7)) // 111   7
console.log (decimalToBinary (8), decimalToOctal (8)) // 1000  10
console.log (decimalToBinary (9), decimalToOctal (9)) // 1001  11

Answer 4

When you call deci(3), y will never become 1, so you will get an infinite loop. The only inputs that does not result in an infinite loop are powers of 2 (1, 2, 4, 8, 16, ...)

To figure out what's going on, add a console.log call inside the while loop.

function deci(y) {
  console.log('converting', y, 'to binary')
  var res = '1'
  while (y != 1) {
    res += y % 2
    y = y / 2
    console.log('y is', y)
    // let's throw an error after a while to avoid freezing the computer
    if (y < 0.001) throw "infinite loop"
  }
  console.log('the result is', res)
}
deci(64)  // this works fine
deci(3)   // this ends up in an infinite loop

In general do not use =! and == with floating point numbers. Since even when your logic seems correct, there might be rounding errors that you would not get with decimal numbers. Is floating point math broken?

To convert a number to base 2, you can use number.toString(2)

function deci(n) {
  return n.toString(2)
}
console.log(deci(3)) // -> '11'