JavaScript - lesson 2 | HackIndia Skills

JavaScript - lesson 2 | HackIndia Skills | HackIndia

Example

Check before using

This is the kind of small guard code recruiters like to see. It shows you know what your code expects.

const amountInput = "499";
const nameInput = "Asha";

const amount = Number(amountInput);

if (typeof nameInput !== "string" || nameInput.trim() === "") {
  throw new Error("Name is required");
}

if (Number.isNaN(amount) || amount <= 0) {
  throw new Error("Amount must be a positive number");
}

console.log(`${nameInput.trim()} paid ₹${amount}`);

Common mistake

Common trap

Do not trust truthy and falsy checks for everything. They are useful, but they can hide valid values.

For example, 0 is falsy. If your app allows a zero balance, if (!balance) will treat it like a missing value. Be specific when the value matters.

const balance = 0;

// Too broad: treats 0 as missing
if (!balance) {
  console.log("Balance missing");
}

// Better: checks only for no value
if (balance === null || balance === undefined) {
  console.log("Balance missing");
}

Example

Small reusable check

You do not need a library for basic validation. A clear helper function is enough for many hackathon projects.

function getPositiveNumber(value, fieldName) {
  if (value === null || value === undefined) {
    throw new Error(`${fieldName} is required`);
  }

  const numberValue = Number(value);

  if (Number.isNaN(numberValue) || numberValue <= 0) {
    throw new Error(`${fieldName} must be a positive number`);
  }

  return numberValue;
}

const ticketPrice = getPositiveNumber("149", "Ticket price");
console.log(ticketPrice + 1);

Values, Types, And Checks

One habit

Values have types

Check before using

Common trap

Safe conversion flow

Use AI carefully

Small reusable check

Do this now

Quick check