I have a string that contains Boolean logic, something along the lines of:
((true && true) || false && !true)
What is the best way in Javascript to safely evaluate this string to get the boolean result? I would like to avoid using eval().
9
2 Answers
I wrote this boolean string parser for another question:
var exp1 = "(true && true || false) && (true || (false && true))";
var exp2 = "((true && true) || false && !true)";
var exp3 = "(true && !false) && true && !false";
var exp4 = "(a && b) && c && d";
console.log(exp1 + ' = ' + parseBoolStr(exp1));
console.log(exp2 + ' = ' + parseBoolStr(exp2));
console.log(exp3 + ' = ' + parseBoolStr(exp3));
console.log(exp4 + ' = ' + parseBoolStr(exp4));
function parseBoolStr(str) {
var expressions = {};
var expressionRegex = new RegExp("\\((?:(?:!*true)|(?:!*false)|(?:&&)|(?:\\|\\|)|\\s|(?:!*\\w+))+\\)");
var expressionIndex = 0;
str = str.trim();
while (str.match(expressionRegex)) {
var match = str.match(expressionRegex)[0];
var expression = 'boolExpr' + expressionIndex;
str = str.replace(match, expression);
match = match.replace('(', '').replace(')', '');
expressions[expression] = match;
expressionIndex++;
}
return evalBoolStr(str, expressions);
}
function evalBoolStr(str, expressions) {
var conditions = str.split(' ');
if (conditions.length > 0) {
var validity = toBoolean(conditions[0], expressions);
for (var i = 1; i + 1 < conditions.length; i += 2) {
var comparer = conditions[i];
var value = toBoolean(conditions[i + 1], expressions);
switch (comparer) {
case '&&':
validity = validity && value;
break;
case '||':
validity = validity || value;
break;
}
}
return validity;
}
return 'Invalid input';
}
function toBoolean(str, expressions) {
var inversed = 0;
while (str.indexOf('!') === 0) {
str = str.replace('!', '');
inversed++;
}
var validity;
if (str.indexOf('boolExpr') === 0) {
validity = evalBoolStr(expressions[str], expressions);
} else if (str == 'true' || str == 'false') {
validity = str == 'true';
} else {
validity = window[str]();
}
for (var i = 0; i < inversed; i++) {
validity = !validity;
}
return validity;
}
function a() {
return false;
}
function b() {
return true;
}
function c() {
return true;
}
function d() {
return false;
}Functions a, b, c and d can, and should, be removed. Just an example.
Usage: parseBoolStr('((true && true) || false && !true)');
Comments
You can use Angular $parse service. Angular parsing expressions, without eval them.
Example of use:
var x=$parse(' ((true && true) || false && !true) ')()
console.log(x) // will return true
ReadMore:
var a=angular.module('app',[])
a.run(function($parse){
alert($parse('true || false || true || false')())
})<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<body ng-app=app>
answered Dec 6, 2015 at 15:20
Aminadav Glickshtein
24.8k13 gold badges84 silver badges118 bronze badges
1 Comment
dfj
This is getting close. Is there an equivalent to this for ReactJS?
eval()you'll have to write a parser for your expression grammar.Function('return ' + expression)()eval()probably doesn't want to use something equivalently dangerous.setTimeout(expressionString,0)but this is like eval