mathjs/docs/reference/functions/parser.md

Math.js is an extensive math library for JavaScript and Node.js. It features a flexible expression parser and offers an integrated solution to work with numbers, big numbers, complex numbers, units, and matrices.

# Function parser

Create a parser. The function creates a new `math.expression.Parser` object.


## Syntax

```js
math.parser()
```

### Parameters

Parameter | Type | Description
--------- | ---- | -----------


### Returns

Type | Description
---- | -----------
Parser | Parser


## Examples

```js
var parser = new math.parser();

// evaluate expressions
var a = parser.eval('sqrt(3^2 + 4^2)'); // 5
var b = parser.eval('sqrt(-4)');        // 2i
var c = parser.eval('2 inch in cm');    // 5.08 cm
var d = parser.eval('cos(45 deg)');     // 0.7071067811865476

// define variables and functions
parser.eval('x = 7 / 2');               // 3.5
parser.eval('x + 3');                   // 6.5
parser.eval('function f(x, y) = x^y');  // f(x, y)
parser.eval('f(2, 3)');                 // 8

// get and set variables and functions
var x = parser.get('x');                // 7
var f = parser.get('f');                // function
var g = f(3, 2);                        // 9
parser.set('h', 500);
var i = parser.eval('h / 2');           // 250
parser.set('hello', function (name) {
  return 'hello, ' + name + '!';
});
parser.eval('hello("user")');           // "hello, user!"

// clear defined functions and variables
parser.clear();
```


## See also

[eval](eval.md),
[compile](compile.md),
[parse](parse.md)


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