JavaScript Global : Object

The following are properties of the global object. They can be accessed from anywhere without additional qualifiers.

Global Properties

Infinity : Number

Positive infinity.

Example:

console.log(Infinity);
console.log(1/0);

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NaN : Number

Floating point Not a Number. Signifies an error in a calculation. NaN is never equal to another Number, even if it is NaN. To check if something is NaN, use isNaN().

Example:

console.log(NaN);
console.log(0/0);
console.log(Math.sqrt(-1));

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undefined : undefined

Returns the undefined type. This value signifies no value has been set on a property or that a method returned no value.

Example:

var x = {};
console.log(x.foo);
var noReturn = function() {};
console.log(noReturn());

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Global Methods

decodeURI(encodedURI : String) : String

Returns a string that is the decoded version of encodeURI.

Example:

console.log(decodeURI('http://foo/bar%20baz'));

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decodeURIComponent(encodedURIComponent : String) : String

Returns a string that is the decoded version of encodeURIComponent.

Example:

console.log(decodeURIComponent('http%3A%2F%2Ffoo%2Fbar%20baz'));

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encodeURI(uri : String) : String

Returns a string that is the encoded version of uri.

Example:

console.log(encodeURI('http://foo/bar baz'));

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encodeURIComponent(component : String) : String

Returns an encoded version of component that is suitable as a uri parameter, such as a query string.

Example:

console.log(encodeURIComponent('http://foo/bar baz'));

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eval(code : String) : Object

Treats code as JavaScript and executes it, returning the result.

Example:

console.log(eval('1 + 1'));

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isFinite(x : Object) : Boolean

Returns true if x is not NaN, +Infinity, or -Infinity. If x is not a Number, it is first converted to a Number before checking if it is finite. Use Number.isFinite(x) to prevent any conversion from happening.

Example:

console.log(Number.isFinite(0/0)); // 0/0 is NaN
console.log(Number.isFinite(1/0)); // 1/0 is infinity
console.log(Number.isFinite(1.2)); // 1.2 is finite

console.log();

// Compare Number.isFinite and global isFinite methods
console.log(Number.isFinite('0')); // '0' is a string, not a Number
console.log(isFinite('0')); // The '0' string is first converted to a Number

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isNaN(x : Number) : Boolean

Returns true if x is NaN. NaN is never equal to another Number, even if it is NaN, so you must use isNaN to check for NaN. If x is not a Number, it is first converted to a Number before checking if it is NaN. Use Number.isNaN(x) to prevent any conversion from happening.

Example:

var x = 0/0;
console.log(x === NaN); 
console.log(isNaN(x)); 

console.log();

// Compare Number.isNaN and global isNaN methods
console.log(Number.isNaN('NaN')); // 'NaN' is a string, not a Number
console.log(isNaN('NaN')); // The 'NaN' string is first converted to a Number

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parseFloat(str : String) : Number

Converts str into a floating point number.

Example:

console.log(parseFloat('3.14') * 2);

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parseInt(str : String, [base : Number]) : Number

Converts str into an integral number. If base is not specified, parseInt will attempt to determine the base to use depending on the input. parseInt is more forgiving than Number(str) (or equivalently +str) in that it will ignore extra characters after the numeric portion of the string. If the first character is not a valid number in the specified base, parseInt will return NaN.

Example:

console.log(parseInt('12'));
console.log(parseInt('0x12'));    // Detected hex
console.log(parseInt('012'));     // Detected octal
console.log(parseInt('012', 10)); // Force decimal

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