5 ways to convert strings to numbers in JavaScript

Tram Ho

Convert from string to số , this you have done many times, right? There are quite a few ways to convert such as:

  • parseInt (x)
  • parseFloat (x)
  • Number (x)
  • + x
  • ~~ x

You may be familiar with parseInt , parseFloat , Number and their names clearly show what they do. The unary plus and Bitwise NOT (double tilde ~~ ) are rarely used by us.

Let’s find out about the difference when convert strings into numbers of 5 ways above

1. Type of the conversion

Convert type

The most obvious difference is the type of result returned by each way. parseInt will always convert to an Integer .

Using ~~ will always return an Integer

parseFloat , + and the Number function will return Integer if possible, and will return Float in the remaining cases.

2. Type of the operand

All of the above can accept a string as input. But what if its input is not a string?

parseInt and parseFloat will always return NaN for any non- string input

Number , + and ~~ can convert boolean values, return 1 if input is true , 0 if input is false

and they will return 0 for null

When the input value is undefined , Number and + will return NaN and ~~ will describe 0

3. Invalid conversions

When the input data is incorrect (wrong format), we will see more than the difference between the above.

parseInt and parseFloat will convert as much as possible, until they find an unverified element.

Number and + will return NaN if the input cannot be converted. As always, ~~ returns an integer – 0 .

The way each operation deals with an empty string is also interesting. All return 0 except parseInt and parseFloat return NaN. It is interesting to convert an empty string. parseInt and parseFloat will return NaN and the rest will return 0

4. Exponents, hex and other bases

parseInt has a nice feature, when you can pass more parameters to the hệ (base) as the second argument. The default is base 10

As for Number , + and ~~ : it doesn’t work

On the other hand, parseInt cannot convert strings with exponential notation, while all other ways are possible. More precisely, parseInt will stop at a character that is not the first number, returning unexpected results:

Unlike the exponent, parseInt works correctly with base-8 system:


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Source : Viblo