Expression.js

Expression.js is an engine for javascript that can compile and evaluate expressions written in typescript.

Installation

Install via npm.

npm install expression.js --save

or yarn.

yarn add expression.js

Getting Started

Example:

import {Evaluator} from "expression.js";

const evaluator = new Evaluator();

// assume your have the following expr.
const expr = "user.ip in allowedIps and user.role is 'admin'";

const context = {
    user: {
        ip: "127.0.0.1",
        role: "admin"
    },
    allowedIps: ["127.0.0.1", "... other ip"]
};

if (evaluator.evaluate(expr, context)) {
    // yes. you're allowed.
    doSomething();
}

Supported binary & unary.

Binary

Operator	Sample
or	alias of `
`
and	alias of &&
&&	a && b
`	`
^	a ^ b
&	a & b
==	a == b
===	a === b
is	alias of ===
!=	a != b
!==	a !== b
<	a < b
>	a > b
>=	a >= b
<=	a <= b
in	10 in [8,10,12]
<<	a << b
>>	a >> b
+	a + b
-	a - b
~	a ~ b
*	a * b
/	a / b
%	a % b

Unary

Operator	Sample
+	+10
-	-10
!	!a
not	alias of !
++	++ a or a ++
--	-- a or a --

Function call.

evaluator.evaluate('say("hello", "world")', {
    say: function (left, right) {
        return left + ' ' + right;
    }
});

// will output "hello world".

Method also supported.

evaluator.evaluate('people.say("hello", "world")', {
    people: {
        say: function (left, right) {
            return left + ' ' + right;
        }
    }
});

You can write multi expressions, separated by SEMICOLON(;); However, evaluator will only return the value of the last expr.

evaluator.evaluate('12; "abc"'); //will ouput "abc"

Assign statement is also supported.

evaluator.evaluate('a = 10; a + 2'); //will ouput 12

LICENSE

The MIT license. See MIT