JavaScript for Excel Users: Arrays, map, filter and reduce Explained

📎 This article includes 2 downloadable practice files ↓

JavaScript runs in every browser, powers Office Scripts and Google Apps Script, and is the language of the web. The fastest way in for an Excel user is through arrays — because a column in Excel is basically an array.

Press F12 in your browser, open the Console tab, and paste the examples.

Your data as an array of objects

const sales = [
  { rep: "Asha",  region: "North", amount: 12500 },
  { rep: "Rohit", region: "South", amount:  8400 },
  { rep: "Meera", region: "North", amount: 15200 },
  { rep: "Karan", region: "East",  amount:  6100 },
];

Each { } is a row; rep, region, amount are the column headers.

filter = AutoFilter / FILTER()

const north = sales.filter(s => s.region === "North");
// Excel: =FILTER(A2:C5, B2:B5="North")

map = a formula column

const withTax = sales.map(s => ({ ...s, tax: s.amount * 0.18 }));
// Excel: new column D with =C2*0.18

reduce = SUM / SUMIFS

const total = sales.reduce((sum, s) => sum + s.amount, 0);             // =SUM(C2:C5)
const northTotal = north.reduce((sum, s) => sum + s.amount, 0);        // =SUMIFS(C:C, B:B, "North")

sort = Sort largest to smallest

const ranked = [...sales].sort((a, b) => b.amount - a.amount);
// Excel: =SORTBY(A2:C5, C2:C5, -1)

Group by = pivot table

const byRegion = {};
for (const s of sales) {
  byRegion[s.region] = (byRegion[s.region] || 0) + s.amount;
}
console.table(byRegion);   // { North: 27700, South: 8400, East: 6100 }

console.table prints a neat table — your first “pivot”.

Where to go next

• Automate Excel on the web with the same syntax: Office Scripts.
• Prefer SQL for data questions? Try the SQL Playground.