If Statements

if (age >= 18) { } else { }

When your program has to choose between doing one thing or another, you need an if.

Think of it as a switch on a railway track: the train of thought arrives, the switch is
checked, and the train goes left or right. It can’t go both ways, and it can’t stop.

let age = 16;

if (age >= 18) {
  allowAccess();
} else {
  denyAccess();
}

age >= 18 is false here, so the train goes right: denyAccess() runs and
allowAccess() never does. Change age to 20 and it goes the other way.

The Two Halves

if (condition) {
  // this runs when the condition is true
} else {
  // this runs when it isn't
}

Exactly one side runs. Never both, never neither.

The else half is optional — leave it off and a false condition simply means nothing
happens.

The Trap: One Equals Sign

if (age = 18) {   // wrong — this assigns 18 to age, then checks if 18 is truthy
if (age === 18) { // right — this compares age to 18

= assigns a value. === compares two values. if (age = 18) doesn’t ask a question at
all — it sets age to 18 and moves on, and since 18 is truthy, that branch always
runs. Always use === inside an if.

Lessons 0/16

▸ View all lessons Start lesson 1 →

○ What Happens? — if #1 guess_type ○ What Happens? — if #2 guess_type ○ What Happens? — if #3 guess_type ○ Memory — the true branch memory_game ○ Memory — the else branch memory_game ○ Valid or invalid? — if #1 guess_type ○ Valid or invalid? — if #2 guess_type ○ Valid or invalid? — if #3 guess_type ○ Which is better? — if #1 snippet_choice ○ Which is better? — if #2 snippet_choice ○ Type It: If/Else type_practice ○ Write It: If/Else exercise ○ Write It: If/Else #2 exercise ○ Write It: If/Else #3 exercise ○ Find the Bug: Missing Parenthesis syntax_game ○ Find the Bug: Missing Brace syntax_game

Tinkr

Documentation

Sections

If Statements

The Two Halves

The Trap: One Equals Sign