Foundations

Arrays

Arrays keep related values in order and let code read values by index.

array index Array indexes start at zero, so `scores[0]` reads the first value.

Arrays

bonus
arrays.js
Replay: real traced execution (multi-file project)
const scores = [82, 91, 76];
const bonus = 5;
const firstScore = scores[0];
const adjustedScore = scores[1] + bonus;

console.log("first=" + firstScore);
console.log("adjusted=" + adjustedScore);

const scores = [82, 91, 76];
const bonus = 0;
const firstScore = scores[0];
const adjustedScore = scores[1] + bonus;

console.log("first=" + firstScore);
console.log("adjusted=" + adjustedScore);

const scores = [82, 91, 76];
const bonus = 10;
const firstScore = scores[0];
const adjustedScore = scores[1] + bonus;

console.log("first=" + firstScore);
console.log("adjusted=" + adjustedScore);

  1. scores ← 82,91,76, bonus ← 5, firstScore ← 82, scores[0] ← 82

    1const scores→ 82,91,76 = [82, 91, 76];2const bonus→ 5 = 5; //@bonus=0, 103const firstScore→ 82 = scores[0]→ 82;4const adjustedScore→ 96 = scores[1]→ 91 + bonus5;56console.log("first=" + firstScore82);7console.log("adjusted=" + adjustedScore96);
    outputfirst=82
adjusted=96

  1. scores ← 82,91,76, bonus ← 0, firstScore ← 82, scores[0] ← 82

    1const scores→ 82,91,76 = [82, 91, 76];2const bonus→ 0 = 0;3const firstScore→ 82 = scores[0]→ 82;4const adjustedScore→ 91 = scores[1]→ 91 + bonus0;56console.log("first=" + firstScore82);7console.log("adjusted=" + adjustedScore91);
    outputfirst=82
adjusted=91

  1. scores ← 82,91,76, bonus ← 10, firstScore ← 82, scores[0] ← 82

    1const scores→ 82,91,76 = [82, 91, 76];2const bonus→ 10 = 10;3const firstScore→ 82 = scores[0]→ 82;4const adjustedScore→ 101 = scores[1]→ 91 + bonus10;56console.log("first=" + firstScore82);7console.log("adjusted=" + adjustedScore101);
    outputfirst=82
adjusted=101

Follow the Array

  1. scores starts as [82, 91, 76].
  2. bonus starts at 5.
  3. firstScore = scores[0] reads 82.
  4. adjustedScore = scores[1] + bonus adds 91 + 5.
  5. The program prints first=82 and adjusted=96. | bonus | first score | adjusted score | | --- | --- | --- | | 0 | 82 | 91 | | 5 | 82 | 96 | | 10 | 82 | 101 |

Exercise: arrays.js

Reproduce first=82 and adjusted=96, then try bonus 0 and 10 and predict each adjusted score before running it.