expression-calculator

expression-calculator

A simple expression parser, using LL(1) syntax analyzer.

Useful to parse and calculate expression without using eval(), so as to avoid all the security risks caused by eval().

API Documentation

Initialization

const calc = new Calc();
const calc = new Calc(expression);
const calc = new Calc(RPN);

Methods

compile(expr)

Compile an expression into an RPN expression.

Parameters

• expr - Expression to compile in string.

Returns

A reference to this instance.

Throws

• SyntaxError - If the given expression contains error.

calc(vars)

Calculate the previously compiled expression.

The compiled expression may contain variables, with default value 0.

You may use a key-value dict to specify values for variables in the expression. Variable names are case sensitive.

Parameters

• vars - A dict contains key-value pairs (Optional).

Returns

The calculation result, or null if no RPN is loaded or compiled from expression.

Example

var calc = new Calc();
calc.compile('3+4').calc(); //Result: 7
calc.compile('3+4-a').calc({a:-10}); //Result: 17

getRPN()

Get the compiled RPN expression.

Returns

Returns the compiled RPN which can be converted into JSON, or undefined if no RPN is loaded or compiled.

Example

var calc = new Calc();
calc.compile('3*(5+a)').getRPN();

The code above will get the following JSON data:

[
	{type:1, value:3},
	{type:1, value:5},
	{type:2, value:"a"},
	{type:3, value:"+"},
	{type:3, value:"*"}
]

In the expression above, each token's type value has an alias, you may refer to Aliases section for detail.

You may also use it to check if the input expression is valid:

var calc = new Calc();
function checkExpr(expr) {
	try {
		var rpn = calc.compile(expr).getRPN();
		for (var i = 0; i < rpn.length; i++) {
			if (rpn[i].type == VAR) {
				return false;
			}
		}
	} catch(e) {
		return false;
	}
	return true;
}

setRPN(expr)

Load previously compiled RPN from other source like database or memcache/redis.

Parameters

• expr - The RPN expression, with the same format as data returned by method getRPN().

Returns

A reference to this instance.

Throws

• SyntaxError - If the given RPN contains invalid tokens or errors.

Aliases

Calc.TOKEN_NUM

Mark RPN tokens as number type.

Calc.TOKEN_VAR

Mark RPN tokens as variable type.

Calc.TOKEN_OPER

Mark RPN tokens as operand type.