JS-0061 · Prefer not to extend native types

Prefer not to extend native types JS-0061

Anti-pattern

Minor

10 months ago — 2 years old

Number prototype is read only, properties should not be added

controllers/excel.controller.js

287
288    //-- Define degrees function
289    if (typeof Number.prototype.toDeg === "undefined") {
290      Number.prototype.toDeg = function () {291        return this * (180 / Math.PI);292      };293    }
294
295    //-- Define middle point function

Number prototype is read only, properties should not be added

controllers/excel.controller.js

280
281    //-- Define radius function
282    if (typeof Number.prototype.toRad === "undefined") {
283      Number.prototype.toRad = function () {284        return (this * Math.PI) / 180;285      };286    }
287
288    //-- Define degrees function

Description

In JavaScript, you can extend any object, including builtin or "native" objects. Sometimes people change the behavior of these native objects in ways that break the assumptions made about them in other parts of the code.

Bad Practice

// seems harmless
Object.prototype.extra = 55;

// loop through some userIds
const users = {
    "123": "Stan",
    "456": "David"
};

// not what you'd expect
for (const id in users) {
    console.log(id); // "123", "456", "extra"
}

In the above example, a common suggestion to avoid this problem would be to wrap the inside of the for loop with users.hasOwnProperty(id).

denizd1 / app

Bad Practice

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