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7 ways to convert a String to Number in JavaScript

Sanchithasr
Web developer
Updated on ・2 min read

1. Using parseInt()

parseInt() parses a string and returns a whole number. Spaces are allowed. Only the first number is returned.
This method has a limitation though. If you parse the decimal number, it will be rounded off to the nearest integer value and that value is converted to string. One might need to use parseFloat() method for literal conversion.

myString = '129' 
console.log(parseInt(myString)) // expected result: 129

a = 12.22
console.log(parseInt(a)) // expected result: 12
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2. Using Number()

Number() can be used to convert JavaScript variables to numbers. We can use it to convert the string too number.
If the value cannot be converted to a number, NaN is returned.

Number("10");          // returns 10
Number(" 10  ");       // returns 10
Number("10.33");       // returns 10.33
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3. Using Unary Operator (+)

The unary plus operator (+) precedes its operand and evaluates to its operand but attempts to convert it into a number, if it isn't already.

const x = 25;
const y = -25;
console.log(+x); // expected output: 25
console.log(+y); // expected output: -25
console.log(+''); // expected output: 0
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4. Using parseFloat()

parseFloat() parses a string and returns a number. Spaces are allowed. Only the first number is returned.

parseFloat("10");        // returns 10
parseFloat("10.33");     // returns 10.33
parseFloat("10 20 30");  // returns 10
parseFloat("10 years");  // returns 10
parseFloat("years 10");  // returns NaN
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5. Using Math.floor()

The Math.floor() function returns the largest integer less than or equal to a given number. This can be little tricky with decimal numbers since it will return the value of the nearest integer as Number.

str = '1222'
console.log(Math.floor(str)) // returns 1222

a = 12.22
Math.floor(a) // expected result: 12
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6. Multiply with number

Multiplying the string value with the 1 which won’t change the value and also it will be converted to number by default.

str = '2344'
console.log(str * 1) // expected result: 2344
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7. Double tilde (~~) Operator

We can use the double tilde operator to convert the string to number.

str = '1234'
console.log(~~str) // expected result: 1234
negStr = '-234'
console.log(~~negStr) // expected result: -234
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Here is the comparison of the ways mentioned performance wise. Comment below if you know more methods.
Thank You

Discussion (5)

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rvxlab profile image
RVxLab • 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.

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raddevus profile image
raddevus

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

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sanchithasr profile image
Sanchithasr Author • Edited

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

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jgburet profile image
Jean-Guillaume Buret

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

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aalphaindia profile image
Pawan Pawar

thanks for the info.