The JavaScript if/else conditional

An if statement picks one path based on a condition. JavaScript evaluates the expression, treats it as true or false, and runs the matching block.

This always runs because the condition is literally true:

if (true) {
  //do something
}

This never runs:

if (false) {
  //do something (? never ?)
}

With a single statement you can skip the block:

if (true) doSomething()

Truthy and falsy

The condition does not need to be true or false. JavaScript converts the value using truthiness rules.

Numbers are truthy except 0 and NaN. Strings are truthy except ''. Objects and arrays are truthy. null and undefined are falsy.

Run this to see the pattern:

if ('hello') console.log('string is truthy')
if (0) console.log('never runs')

The first line prints. The second does not.

Else

Add else for the false branch:

if (true) {
  //do something
} else {
  //do something else
}

else accepts one statement, so you can nest another conditional:

if (a === true) {
  //do something
} else if (b === true) {
  //do something else
} else {
  //fallback
}

Read conditions from top to bottom. The first match wins. Put the most specific checks first and broad fallbacks last.

Blocks create scope for let and const. A variable declared inside if is not visible outside it.

You can chain else if as many times as you need. Keep each branch small. When a branch grows past a few lines, extract a function with a descriptive name.

Ternary expressions fit simple assignments. Multi-step branches belong in if/else blocks where you can log and debug each path.

My advice: prefer explicit comparisons when the input might be 0 or ''. if (count) treats zero as false even when zero is valid data.

Try this: write an if/else that sets label to 'empty' for '', 'zero' for 0, and 'ok' for any other string. Log each case and confirm the branch you expected.