Javascript Most frequent Errors — Guide — Reason and Options to fix

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Debugging is an art and it is very important that we use right tools, reading errors is big assest which gives a clear information on what went wrong.

not defined

console.log(tax);
tax is not defined

It is a reference error and whenever we use a variable, it should be either declared or defined in the same file or imported from a file where it is declared or defined and exported

const tax = 10 — Option 1

let tax — Option 2

import {tax} from 'somefile' — Option 3

Cannot read properties of undefined (reading ‘something’)

let user;
console.log(user.name)

Value of the user is undefined, we try to access properties of an undefined variable, we get this.

We can either user ? or we need to define the variable as object

console.log(user?.name) — Option 1

let user={} — Option 2

let user={name:'Vinodh'} — Option 3

Cannot read properties of null (reading ‘something’)