Hello everyone! π
This is my first post here. After facing significant challenges while trying to eliminate unsafe-eval from an existing application's Content Security Policy (CSP), I finally developed a robust and generic solution that other developers can easily adopt and extend. To support the dev community, Iβm excited to share the steps I followed to accomplish this.
Step 1: Replacing unsafe-eval Using mathjs
I found that mathjs is a powerful tool that can replace the need for eval in evaluating mathematical expressions.
Steps:
Install mathjs:
npm install mathjs
Import and configure mathjs:
const { create, all } = require('mathjs');
const math = create(all);
Set up custom functions:
math.import(
{
YOURFUNC: YOURFUNC,
ADD: (a, b) => a + b,
parseInt
},
{ override: true }
);
// Create a scope object
const scope = {
x: 3,
y: 4
};
try {
evaluateValue = math.evaluate(exp, scope);
} catch (error) {
// If `mathjs` cannot evaluate, proceed with the next approach
}
Success! π The code above should work for the following expressions, producing the same results as eval:
let exp;
exp = '1 + 2'; // Output: 3
exp = 'ADD(1, 2)'; // Output: 3
exp = '2 + 3 + parseInt(4.5)'; // Output: 9
exp = 'x * y' // Output: 12
Step 2: Handling Complex Expressions if mathjs Fails
If mathjs cannot handle complex expressions that involve object properties, try this approach:
Solution:
Replace expressions dynamically:
const replacedExp = exp => exp.replace(/myObject\["([^"]+)"\]/g, (_, key) => JSON.stringify(data[key] || ''));
const myObject = {
a: "test1",
"a.b": "test2",
"a.b.c": "test3",
2: "test4"
};
// Examples
console.log(myObject["a"]); // Output: "test1"
console.log(myObject["a.b"]); // Output: "test2"
console.log(myObject["a.b.c"]); // Output: "test3"
console.log(myObject[2]); // Output: "test4"
This approach should help you safely handle complex object expressions without resorting to eval.
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