Values, Types, and Expressions

Primitive Types

Work with numbers and booleans, and read a value's type.

primitive-types Numbers and booleans are primitive values. A comparison yields a boolean, and `typeof` reports the type name as a string.

Primitive Types

n
primitive_types.js
Replay: real traced execution (multi-file project)
const n = 42;
const big = n > 10;
const kind = typeof n;

console.log("n=" + n);
console.log("big=" + big);
console.log("kind=" + kind);

const n = 7;
const big = n > 10;
const kind = typeof n;

console.log("n=" + n);
console.log("big=" + big);
console.log("kind=" + kind);

const n = 100;
const big = n > 10;
const kind = typeof n;

console.log("n=" + n);
console.log("big=" + big);
console.log("kind=" + kind);

  1. n ← 42, big ← true, kind ← number

    1const n→ 42 = 42; //@n=7, 1002const big→ true = n→ 42 > 10;3const kind→ number = typeof n;45console.log("n=" + n42);6console.log("big=" + bigtrue);7console.log("kind=" + kindnumber);
    outputn=42
big=true
kind=number

  1. n ← 7, big ← false, kind ← number

    1const n→ 7 = 7;2const big→ false = n→ 7 > 10;3const kind→ number = typeof n;45console.log("n=" + n7);6console.log("big=" + bigfalse);7console.log("kind=" + kindnumber);
    outputn=7
big=false
kind=number

  1. n ← 100, big ← true, kind ← number

    1const n→ 100 = 100;2const big→ true = n→ 100 > 10;3const kind→ number = typeof n;45console.log("n=" + n100);6console.log("big=" + bigtrue);7console.log("kind=" + kindnumber);
    outputn=100
big=true
kind=number

Follow the Primitives

  1. n starts at 42.
  2. big = n > 10 becomes true.
  3. kind = typeof n becomes number.
  4. The program prints n=42, big=true, and kind=number. | n | big | kind | | --- | --- | --- | | 7 | false | number | | 42 | true | number | | 100 | true | number |

Exercise: primitive_types.js

Reproduce big=true and kind=number for n=42, then use the pinned n values 7 and 100 to predict big.