Convert string to either integer or float in javascript

Question

Is there a straightforward way to parse a string to either integer or float if I don't know if the variable is integer-number-like or decimal-number-like?

a = '2'; // => parse to integer
b = '2.1'; // => parse to float
c = '2.0'; // => parse to float
d = 'text'; // => don't parse

EDIT: It seems my question lacked the necessary context: I want to do some calculations without losing the original format (Original format thereby means integer vs. float. I don't care about the original number of decimal places):

Example:

String containing the formatted number ('2') => parse to number (2.0) => do some calculations (2.0 + 1 = 3.0) => restore "original format" ('3' and not '3.0')

If the input was 2.0 instead, the wanted result would be '3.0' (not '3').

Why do you wan't to parse? Javascript has dynamic typing. Moreover, the only numerical type it has is double. — david a., Nov 05 '15 at 12:43
@david a.: Thanks for pointing that out. I wasn't aware of that. Still wondering why there are two functions (parseInt, parseFloat) in JavaScript if there is only one numerical type. — am2124429, Dec 01 '15 at 14:39
I think that the difference is just how the two parse the input - `parseInt()` only takes the integer part of it, while `parseFloat()` takes the decimal (and perhaps the exponent) as well. They, however, both return the same type (number, that is actually a floating-point type). See spec of JS numbers here: http://www.ecma-international.org/ecma-262/6.0/index.html#sec-terms-and-definitions-number-value . MSDN mentions the same thing here: https://msdn.microsoft.com/library/7wkd9z69(v=vs.94).aspx#Anchor_4 — david a., Dec 01 '15 at 17:34
as there is no difference between a float and an int, you can really just do: `isNaN(val) ? val : parseFloat(val);` — Mortimer, Aug 11 '17 at 05:55

score 19 · Answer 1 · answered Nov 05 '15 at 12:43

19

Multiply string which has number data with 1. You will get the Numeric data value.

var int_value = "string" * 1;

In your case

a = '2' * 1; // => parse to integer
b = '2.1' * 1; // => parse to float
c = '2.0' * 1; // => parse to float
d = 'text' * 1; // => don't parse    //NaN value

For last one you will get NaN value. Manually handle for NaN value

answered Nov 05 '15 at 12:43

rajuGT

6,224
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This is also the fastest way to do this, by far, even compared to JSON.parse. – Ten Bitcomb Jul 14 '17 at 03:26
You can also prepend a `+`, e.g. `+'2.1'` returns `2.1`. – Ollie Jan 28 '21 at 23:08

score 9 · Answer 2 · answered May 21 '18 at 15:17

9

Just wrap it in Number()

Number('123') === 123

Number('-123.456') === -123.456

answered May 21 '18 at 15:17

D G

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score 0 · Accepted Answer · answered Feb 01 '16 at 14:16

That's how I finally solved it. I didn't find any other solution than to add the variable type to the variable ...

var obj = {
 a: '2',
 b: '2.1',
 c: '2.0',
 d: 'text'
};
// Explicitly remember the variable type
for (key in obj) {
  var value = obj[key], type;
  if ( isNaN(value) || value === "" ) {
    type = "string";
  }
  else {
    if (value.indexOf(".") === -1) {
      type = "integer";
    }
    else {
      type = "float";
    }
    value = +value; // Convert string to number
  }
  obj[key] = {
    value: value,
    type: type
  };
}
document.write("<pre>" + JSON.stringify(obj, 0, 4) + "</pre>");

score 0 · Answer 4 · answered Apr 15 '20 at 15:15

You can use:

function parse(x){
  return x==x*1?x*1:x
 }

function parse(x){
  return x==x*1?x*1:x
 }
 
 console.log(parse(1),typeof parse(1))
 console.log(parse("1"),typeof parse("1"))
 console.log(parse("1.1"),typeof parse("1.1"))
 console.log(parse("1A"),typeof parse("1A"))

Convert string to either integer or float in javascript

4 Answers4

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