Sketch script to scale layers/group individually.

scaleIndividually.js

const sketch = require('sketch/dom');
const UI = require('sketch/ui');
const document = sketch.getSelectedDocument();
const selection = document.selectedLayers.layers.slice();

const resize = (layer, options = {}) => {
    const { scaleX, scaleY, originX, originY } = Object.assign({
    scaleX: 1,
    scaleY: 1,
    originX: 0,
    originY: 0,
}, options);
    const { x, y, width, height } = layer.frame;
    
    const newWidth = width * scaleX;
    const newHeight = height * scaleY;

    const newX = (width - newWidth) * originX + x;
    const newY = (height - newHeight) * originY + y;

    layer.frame.width = newWidth;
    layer.frame.height = newHeight;
    layer.frame.x = newX;
    layer.frame.y = newY;
}

const originXDict = {
    'left': 0,
    'center': 0.5,
    'right': 1,
};

const originYDict = {
    'top': 0,
    'center': 0.5,
    'bottom': 1,
}

const originOptions = [];
const originXKeys = Object.keys(originXDict);
const originYKeys = Object.keys(originYDict);

originYKeys.forEach(keyY => {
    originXKeys.forEach(keyX => {
        originOptions.push(keyY + ` ` + keyX);
    })
})


const stringScale = UI.getStringFromUser('Enter scale', '');
const [ _, selectedOrigin, ok ] = UI.getSelectionFromUser('Enter origin', originOptions);

if (!!stringScale && ok) {
    const scale = Number.parseFloat(stringScale);
    const [ keyY, keyX ] = originOptions[selectedOrigin].split(' ');
    console.log(keyY, keyX);
    selection
        .forEach(l => resize(l, {
            scaleX: scale, 
            scaleY: scale,
            originX: originXDict[keyX],
            originY: originYDict[keyY],
        }))

    UI.message(`Updated ${selection.length} layers.`);
};