Converting a double to an int in Javascript without rounding

Question

In C# the following code returns 2:

double d = 2.9; int i = (int)d; Debug.WriteLine(i); 

In Javascript, however, the only way of converting a "double" to an "int" that I'm aware of is by using Math.round/floor/toFixed etc. Is there a way of converting to an int in Javascript without rounding? I'm aware of the performance implications of Number() so I'd rather avoid converting it to a string if at all possible.

Answer 1

Use parseInt().

var num = 2.9 console.log(parseInt(num, 10)); // 2 

You can also use |.

var num = 2.9 console.log(num | 0); // 2 

Answer 2

I find the "parseInt" suggestions to be pretty curious, because "parseInt" operates on strings by design. That's why its name has the word "parse" in it.

A trick that avoids a function call entirely is

var truncated = ~~number; 

The double application of the "~" unary operator will leave you with a truncated version of a double-precision value. However, the value is limited to 32 bit precision, as with all the other JavaScript operations that implicitly involve considering numbers to be integers (like array indexing and the bitwise operators).

edit — In an update quite a while later, another alternative to the ~~ trick is to bitwise-OR the value with zero:

var truncated = number|0;