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7 ways to convert a String to Number in JavaScript

Sanchithasr on December 16, 2020

1. Using parseInt() parseInt() parses a string and returns a whole number. Spaces are allowed. Only the first number is returned. This m...

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RVxLab • Dec 16 '20 • Edited

The double tilde method is actually something I never thought about, but is worth explaining.

The double tilde "operator" is not as much as an operator as it's a double bitwise negation.

Let's cast '64' to 64 using this method, so we do ~~'64'. First we will evaluate ~'64'. As bitwise operations work on binary, '64' is cast to a number. So ~64.

64 in binary is 01000000. ~ will negate all the bits so it becomes 10111111, which is -65 since numbers in JavaScript are signed. Now we negate it again, which becomes 01000000, which is 64 in decimal.

Correction:

I previously stated that 10111111 is -63, which is incorrect. It's actually -65. Sorry about that.

raddevus • Dec 16 '20

Thanks for explaining this. When I got to that one, I was wondering what it was. Great explanation.

Sanchithasr • Dec 16 '20 • Edited

Thank you. This was informative. I didn't pay attention about how it works while writing. Will note it down.

Juan Ocho • Dec 3 '21

In the first paragraph "If you parse the decimal number, it will be rounded off to the nearest integer value and that value is converted to string. " I think it should say "that value is converted to a number".

Jean-Guillaume Buret • Dec 18 '20

You should always pass the base as second argument to parseInt.

FitGAG • Apr 4 '23

This is a really helpful article! As a beginner in JavaScript, I often find myself struggling with converting strings to numbers. It's great to see all these different methods laid out with examples for each one. I especially appreciated the explanation of the parseFloat() function and the caution against using the unary plus operator on strings that could be mistaken for numbers. Thank you for sharing! FitGAG

Pawan Pawar • Dec 16 '20

thanks for the info.

Junaid • Jun 2 '22

how would we go about converting a 19 digit string to a number , js behaves very weirdly for that
e.g lets say this is the number 6145390195186705543 and want to convert it into number what it gives me is this 6145390195186705000. not sure why

clevewren • Mar 12

Choosing the best method depends on your specific needs. If you need an integer, use parseInt. If you need a floating-point number, use parseFloat. Number() is a good general-purpose option, while the unary plus operator and multiplication by 1 are convenient for quick conversions but might have unexpected behavior. Remember to handle potential NaN results for robustness. Slope 3 is so addictive! I can't stop trying to beat my high score