Javascript parseInteger() to Int32?

Question

I'm trying to convert an integer to Int32 in Javascript (similar to how you'd convert a string to an integer using parseInteger()), however I cannot find the appropriate method. How can I do this?

Answer 1

JavaScript's number type is IEEE-754 double-precision binary floating point; it doesn't have an integer type except temporarily during some math operations or as part of a typed array (Int32Array, for instance, or a Uint32Array if you mean unsigned). So you have two options:

1. Ensure that the number has a value that fits in a 32-bit int, even though it's still a number (floating point double). One way to do that is to do a bitwise OR operation with the value 0, because the bitwise operations in JavaScript convert their operands to 32-bit integers before doing the operation:

   | 0 does a signed conversion using the specification's ToInt32 operation:

   value = value | 0;
   // Use `value`...
   

   With that, -5 becomes -5. 123456789123 becomes -1097262461 (yes, negative).

   or >>> 0 does an unsigned conversion using the spec's ToUint32:

   value = value >>> 0;
   // Use `value`...
   

   The latter converts to unsigned 32-bit int. -5 becomes 4294967291, 123456789123 becomes 3197704835.

2. Use an Int32Array or Uint32Array:

   const a = new Int32Array(1); // Or use Uint32Array for unsigned
   a[0] = value;
   // Use `a[0]`...
   

   Int32Array uses ToInt32, Uint32Array uses ToUint32.

   Note that any time you use a[0], it will be converted back to a standard number (floating point double), but if you use the array, depending on what you use it for, it will get used as-is.

Note that there's a method that may seem like it's for doing this, but isn't: Math.fround. That doesn't convert to 32-bit int, it converts to 32-bit float (IEEE-754 single-precision floating point). So it isn't useful for this.

Answer 2

Well, the easiest way I found is using bitwise not ~.

This is the description from MDN:

The operands are converted to 32-bit integers and expressed by a series of bits (zeroes and ones).

So you can just type double ~ to convert your numbers. Here's some examples:

~~1 // 1
~~-1 // -1
~~5.05 // 5
~~-5.05 // -5
~~2147483647 // 2147483647
~~2147483648 // -2147483648
~~Math.pow(2, 32) // 0