javascript : 5 common error messages

Debugging is a skill to learn. It takes time, it takes practice. It starts by reading error/warning messages.

In JS following 2 messages are not same:
1) undefined
2) uncaught ReferenceError: x is not defined

❌undefined -> During memory creation phase, memory is allocated to each variable. If variable is not initialized, undefined is assigned to that variable.

❌ReferenceError -> uncaught ReferenceError: x is not defined -> It means x is not defined, When JS is in code execution phase and it looks for x in memory but x is not found so it throws this error.

❌TypeError -> Uncaught TypeError: Assignment to constant variable.
const name = 'JavaScript'
name = 'typescript'
Above code throws following error: Uncaught TypeError: Assignment to constant variable.

❌TypeError -> Uncaught TypeError: (intermediate value).disply is not a function

class Main {
display() {
console.log("Hello World");
}
}

new Main().disply(); // it is not a method of Main class
If we are trying to call a method that is not present or callable, then JS will throw a TypeError.

❌SyntaxError -> Uncaught SyntaxError: Missing initializer in const declaration

const javascript
Above code throws following error: Uncaught SyntaxError: Missing initializer in const declaration