This job posting is for a Lead JavaScript Developer position at a fast-growing London startup. The company is seeking a front-end developer to help develop cutting-edge software solutions for their e-commerce and advertising platforms. Responsibilities include implementing web, tablet, and mobile applications; delivering responsive interfaces using front-end skills; mentoring junior developers; and helping scale the front-end architecture. The ideal candidate has skills in JavaScript, HTML5, CSS3, testing frameworks, and tools like Grunt and Gulp.