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Conditional constructs

JavaScriptJunior~1 min read
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1. if, else if, else

This is the main and most readable construct for branching code.

javascript
const age = 20; if (age >= 18) { console.log('Adult'); } else if (age >= 14) { console.log('Teenager'); } else { console.log('Child'); }
  • if checks a condition
  • else if adds additional checks
  • else runs if all the previous ones did not match

The condition inside if is converted to a boolean value (truthy/falsy).

2. The ternary operator ? :

A short form for simple conditions.

javascript
const age = 18; const status = age >= 18 ? 'Adult' : 'Minor'; console.log(status); // "Adult"

Syntax: condition ? value_if_true : value_if_false

You can nest several ternary operators (but be careful with readability):

javascript
const age = 25; const group = age < 13 ? 'child' : age < 20 ? 'teenager' : 'adult';

3. The switch statement

Convenient when there are many variants of the same expression.

javascript
const day = 3; switch (day) { case 1: console.log('Monday'); break; case 2: console.log('Tuesday'); break; case 3: console.log('Wednesday'); break; default: console.log('Unknown day'); }
  • break prevents "falling through" into the next case
  • default is the equivalent of else

You can use grouping:

javascript
switch (day) { case 6: case 7: console.log('Day off'); break; default: console.log('Workday'); }

4. The logical operators &&, ||, ??

Sometimes if can be replaced with logical shorthand.

&&: "and" (runs the second operand if the first is true)

javascript
const isAdmin = true; isAdmin && console.log('Welcome, admin!');

If isAdmin === true, console.log will run.

||: "or" (returns the first truthy value)

javascript
const userName = '' || 'Guest'; console.log(userName); // "Guest"

Convenient for default values.

??: "nullish coalescing" (only for null and undefined)

javascript
const userInput = null; const value = userInput ?? 'Default'; console.log(value); // "Default"

Difference from ||: it does not trigger on 0, '', false.

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