JavaScript Casting Tricks

Here I want to go through some casting tricks that can be used for better data manipulation.

Booleans

Build in Boolean()

The easiest way is to use the builtin Boolean() method.

Boolean('true'); // true
Boolean(1); // true

Boolean('false'); // true !!!!GOTCHA!!!!!
Boolean(0); // false

// Careful
Boolean([]); // true

Double Negative

This will cast anything as either true or false, there are of course a few quirks that may not be obvious.

// FALSE
!!false;
!!null;
!!undefined;
!!0;
!!'';

// TRUE
!!true;
!!'true';
!!1;
!!-1;
!!{};
!!function(){};


// GOTCHA!!! ... TRUE
!!'false';

JSON.parse

This will parse the text 'true' to the boolean true

// TRUE
JSON.parse('true');

// FALSE
JSON.parse('false');

// If using a variable, you'll want a fallback
JSON.parse(undefined || 'true');
JSON.parse('' || 'true');

Numbers

Check for a decimal using modulo

5.5 % 1 != 0; // true
5 % 1 != 0; // false

Reference: http://stackoverflow.com/a/2304062/179335

Strings

Built in tools toString() and String()

var hello = String('hello')
10.0.toString();

Casting an Array as a String

Strings are of course mostly just an array of characters so arrays and strings have a lot in common. You can cast an array to a string simply by joining them with nothing.

var hello = ['h', 'e', 'l', 'l', 'o'];
hello.join('');  // Yields "hello"

Convert from an Array to a String

Strings can be converted to an array easily using split. Here’s how.

var hello = "hello";
hello.split('');  // ['h', 'e', 'l', 'l', 'o'];

Arguments

In JavaScript the arguments object in a function is array like, but to convert it to an actually array you can just use a simple trick.

Array.prototype.slice.call(arguments);

Or more simply if Array generics are available (like in node.js).

Array.slice(arguments);

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