Is there a way to calculate a formula stored in a string in JavaScript without using eval?
Normally I would do something like
var apa = "12/5*9+9.4*2";
alert(eval(apa));
So, does anyone know about alternatives to eval?
Calculate string value in javascript, not using eval
Viewed 99582
13 Answers
This solution also clips whitespaces and checks for duplicating operators
e.g. ' 1+ 2 *2' // 5 but ' 1 + +2* 2 ' // Error
function calcMe(str) {
const noWsStr = str.replace(/\s/g, '');
const operators = noWsStr.replace(/[\d.,]/g, '').split('');
const operands = noWsStr.replace(/[+/%*-]/g, ' ')
.replace(/\,/g, '.')
.split(' ')
.map(parseFloat)
.filter(it => it);
if (operators.length >= operands.length){
throw new Error('Operators qty must be lesser than operands qty')
};
while (operators.includes('*')) {
let opIndex = operators.indexOf('*');
operands.splice(opIndex, 2, operands[opIndex] * operands[opIndex + 1]);
operators.splice(opIndex, 1);
};
while (operators.includes('/')) {
let opIndex = operators.indexOf('/');
operands.splice(opIndex, 2, operands[opIndex] / operands[opIndex + 1]);
operators.splice(opIndex, 1);
};
while (operators.includes('%')) {
let opIndex = operators.indexOf('%');
operands.splice(opIndex, 2, operands[opIndex] % operands[opIndex + 1]);
operators.splice(opIndex, 1);
};
let result = operands[0];
for (let i = 0; i < operators.length; i++) {
operators[i] === '+' ? (result += operands[i + 1]) : (result -= operands[i + 1])
}
return result
}
This shows to be more performant than @vol7ron's solution.
Check this JSBenchmark
I spent a couple of hours to implement all the arithmetical rules without using eval() and finally I published a package on npm string-math. Everything is in the description. Enjoy
If you're looking for a syntactical equivalent to eval, you could use new Function. There are slight differences regarding scoping, but they mostly behave the same, including exposure to much of the same security risks:
let str = "12/5*9+9.4*2"
let res1 = eval(str)
console.log('res1:', res1)
let res2 = (new Function('return '+str)())
console.log('res2:', res2)Note : There is no library used in this solution purely hard coded
My solution takes into account of brackets also like 8+6(7(-1)) or 8+6(7(-1))
You can do these operations ^, *, /, +, -
To calculate a string use calculate(tokenize(pieval("8+6(7(-1))").join("")))
function tokenize(s) {
// --- Parse a calculation string into an array of numbers and operators
const r = [];
let token = '';
for (const character of s) {
if ('^*/+-'.indexOf(character) > -1) {
if (token === '' && character === '-') {
token = '-';
} else {
r.push(parseFloat(token), character);
token = '';
}
} else {
token += character;
}
}
if (token !== '') {
r.push(parseFloat(token));
}
return r;
}
function calculate(tokens) {
// --- Perform a calculation expressed as an array of operators and numbers
const operatorPrecedence = [{'^': (a, b) => Math.pow(a, b)},
{'*': (a, b) => a * b, '/': (a, b) => a / b},
{'+': (a, b) => a + b, '-': (a, b) => a - b}];
let operator;
for (const operators of operatorPrecedence) {
const newTokens = [];
for (const token of tokens) {
if (token in operators) {
operator = operators[token];
} else if (operator) {
newTokens[newTokens.length - 1] =
operator(newTokens[newTokens.length - 1], token);
operator = null;
} else {
newTokens.push(token);
}
}
tokens = newTokens;
}
if (tokens.length > 1) {
console.log('Error: unable to resolve calculation');
return tokens;
} else {
return tokens[0];
}
}
function pieval(input) {
let openParenCount = 0;
let myOpenParenIndex = 0;
let myEndParenIndex = 0;
const result = [];
for (let i = 0; i < input.length; i++) {
if (input[i] === "(") {
if (openParenCount === 0) {
myOpenParenIndex = i;
// checking if anything exists before this set of parentheses
if (i !== myEndParenIndex) {
if(!isNaN(input[i-1])){
result.push(input.substring(myEndParenIndex, i) + "*");
}else{
result.push(input.substring(myEndParenIndex, i));
}
}
}
openParenCount++;
}
if (input[i] === ")") {
openParenCount--;
if (openParenCount === 0) {
myEndParenIndex = i + 1;
// recurse the contents of the parentheses to search for nested ones
result.push(pieval(input.substring(myOpenParenIndex + 1, i)));
}
}
}
// capture anything after the last parentheses
if (input.length > myEndParenIndex) {
result.push(input.substring(myEndParenIndex, input.length));
}
//console.log(cal(result))
let response = cal(result);
return result;
}
function cal(arr) {
let calstr = "";
for (let i = 0; i < arr.length; i++) {
if (typeof arr[i] != "string") {
if (cal(arr[i]) < 0) {
arr[i] = `${cal(arr[i])}`;
} else {
arr[i] = `${cal(arr[i])}`;
}
}
if (typeof arr[i] === "string") {
calstr += arr[i];
}
if (i == arr.length - 1) {
//console.log("cal" ,calstr,calculate(tokenize(calstr)) );
return calculate(tokenize(calstr));
}
}
}
console.log(calculate(tokenize(pieval("8+6(7(-1))").join("")))); // ["1+",["2-",["3+4"]]]
console.log(calculate(tokenize(pieval("1+(1+(2(4/4))+4)").join("")))); // ["1+",["2-",["3+4"]]]There is also an open source implementation on GitHub, evaluator.js, and an NPM package.
From the README: Evaluator.js is a small, zero-dependency module for evaluating mathematical expressions.
All major operations, constants, and methods are supported. Additionally, Evaluator.js intelligently reports invalid syntax, such as a misused operator, missing operand, or mismatched parentheses.
Evaluator.js is used by a desktop calculator application of the same name. See a live demo on the website.
stringToMath(str);
I am using stringToMath(str) instead of eval(), it is working alright to calculate simple string values.
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