const block = $('.block');

const header = $('.header');

​

block.on('click', handleBlockClick);

header.on('click', handleHeaderClick);

​

​

function handleBlockClick() {

    toggleModifierFor(this, '_bgcolor_crimson');

}

​

function handleHeaderClick() {

    toggleModifierFor(this, '_fz_2em');

}

​

function toggleModifierFor(target, modifier) {

    const $this = $(target);

    const b = target.classList[0];

​

  $this.toggleClass( b + modifier);

}

​