JavaScript Heap Out of Memory Error

Use the --max-old-space-size flag to allocate more memory.

# Increase to 4GB
node --max-old-space-size=4096 app.js

# Set in package.json
"scripts": {
  "start": "node --max-old-space-size=4096 app.js"
}

Process files line by line or in chunks instead of loading everything into memory.

const fs = require("fs")
const readline = require("readline")

// ❌ Loads entire file into memory
const data = JSON.parse(fs.readFileSync("large-file.json", "utf-8"))

// ✅ Process with streams
const rl = readline.createInterface({
  input: fs.createReadStream("large-file.json"),
  crlfDelay: Infinity
})

rl.on("line", (line) => {
  const row = JSON.parse(line)
  // Process one row at a time
})

Use heap snapshots to find objects that are not being garbage collected.

# Take heap snapshot
node --inspect app.js
# Open chrome://inspect in Chrome

# Monitor memory usage
const used = process.memoryUsage()
console.log(`Heap used: ${(used.heapUsed / 1024 / 1024).toFixed(2)} MB`)
console.log(`Heap total: ${(used.heapTotal / 1024 / 1024).toFixed(2)} MB`)