An example of 'Insert line numbers' macro for VSCodeMacros extension

InsertLineNumbers.js

// [VSCode Macros] extension
// https://marketplace.visualstudio.com/items?itemName=EXCEEDSYSTEM.vscode-macros
// License:MIT
const vscode = require('vscode');

/**
 * Macro configuration
 */
module.exports.macroCommands = {
    InsertLineNumbers: {
        no: 1,
        func: insertLineNumbers,
    },
};

/**
 * Insert line numbers
 */
async function insertLineNumbers() {
    const editor = vscode.window.activeTextEditor;
    if (editor) {
        const document = editor.document;
        const selection = editor.selection;
        const text = document.getText(selection);
        if (text.length > 0) {
            const firstLineNumberAsString = await vscode.window.showInputBox({
                value: 1,
                prompt: 'Please enter the start line number.'
            });
            if (firstLineNumberAsString === undefined)
                return 'Cancelled.';
            let firstLineNumber = parseInt(firstLineNumberAsString);
            if (isNaN(firstLineNumber))
                return 'Invalid line number.';
            editor.edit((editBuilder) => {
                let resultText = '';
                let currentLineNumber = firstLineNumber;
                // Add the line number to the first line.
                resultText += formatLineNumber(currentLineNumber++);
                for (let code of text) {
                    resultText += code;
                    if (code === '\n') {
                        // If code is LF then append the line number.
                        resultText += formatLineNumber(currentLineNumber++);
                    }
                }
                // Replace the selected text with line-numbered text.
                editBuilder.replace(selection, resultText.toString());
            });
        }
    }

    // Convert the line number to your preferred format.
    function formatLineNumber(lineNumber) {
        return `${lineNumber}. `;
    }
}