test-1.js

const path = require('path');
const fs = require('fs');
const Canvas = require('canvas');

const targetWidth = 6000;
const targetHeight = 50;
const deltaX = 50;

const sourceWidth = deltaX * 20
const sourceHeight = targetHeight * 20;

const sourceCanvas = new Canvas(sourceWidth, sourceHeight);
sourceCanvas.getContext('2d').fillStyle = 'red';
sourceCanvas.getContext('2d').fillRect(0, 0, sourceWidth, sourceHeight);

const targetCanvas = new Canvas(targetWidth, targetHeight);
targetCanvas.getContext('2d').fillStyle = 'blue';
targetCanvas.getContext('2d').fillRect(0, 0, targetWidth, targetHeight);

for (let x = 0; x < targetWidth; x = x + deltaX) {
    targetCanvas.getContext('2d').drawImage(
        sourceCanvas,
        0,
        0,
        sourceWidth,
        sourceHeight,
        x,
        0,
        deltaX,
        targetHeight
    );
}

fs.writeFileSync(
    path.join(__dirname, 'target.png'), 
    new Buffer(
        targetCanvas.toDataURL('image/png').replace(/^data.*?;base64,/, ''),
        'base64'
    )
);

test-2.js

const path = require('path');
const fs = require('fs');
const { createCanvas } = require('canvas');

const targetWidth = 6000;
const targetHeight = 50;
const deltaX = 50;

const sourceWidth = deltaX * 20
const sourceHeight = targetHeight * 20;

const sourceCanvas = createCanvas(sourceWidth, sourceHeight);
sourceCanvas.getContext('2d').fillStyle = 'red';
sourceCanvas.getContext('2d').fillRect(0, 0, sourceWidth, sourceHeight);

const targetCanvas = createCanvas(targetWidth, targetHeight);
targetCanvas.getContext('2d').fillStyle = 'blue';
targetCanvas.getContext('2d').fillRect(0, 0, targetWidth, targetHeight);

for (let x = 0; x < targetWidth; x = x + deltaX) {
    targetCanvas.getContext('2d').drawImage(
        sourceCanvas,
        0,
        0,
        sourceWidth,
        sourceHeight,
        x,
        0,
        deltaX,
        targetHeight
    );
}

fs.writeFileSync(
    path.join(__dirname, 'target.png'), 
    new Buffer(
        targetCanvas.toDataURL('image/png').replace(/^data.*?;base64,/, ''),
        'base64'
    )
);