Build a QR Code Generator with Canvas API — No Libraries Needed

Why No Library? Most QR code generators use qrcode.js or similar. But the Canvas API is powerful enough to do it from scratch, and you eliminate a dependency. How QR Codes Work A QR code is a 2D matrix of modules (black/white squares) that encode data using Reed-Solomon error correction. The key steps: Encode the data into a binary stream Apply error correction (Reed-Solomon) Place modules in the matrix following the QR spec Add finder patterns (the three big squares in corners) Render to Canvas Canvas Implementation function renderQR ( canvas , data , size = 256 ) { const ctx = canvas . getContext ( ' 2d ' ); canvas . width = size ; canvas . height = size ; // Generate QR matrix (simplified) const matrix = generateMatrix ( data ); const moduleSize = size / matrix . length ; // White background ctx . fillStyle = ' #FFFFFF ' ; ctx . fillRect ( 0 , 0 , size , size ); // Draw modules ctx . fillStyle = ' #000000 ' ; for ( let row = 0 ; row < matrix . length ; row ++ ) { for ( let col = 0 ;