for (var i = 0; i < 4; i++) {
  document.write('<div onClick="console.log(i)">i</div>');
}


--------------------------------------------------------------------------------


var start = new Date();

function a1000() {
    console.log('a', (new Date()) - start);
    // 1000ms sync process
    console.log('a', (new Date()) - start);
}

function b2000() {
    console.log('b', (new Date()) - start);
    // 2000ms sync process
    console.log('b', (new Date()) - start);
}

function c3000() {
    console.log('c', (new Date()) - start);
    // 3000ms sync process
    console.log('c', (new Date()) - start);
}

function d4000() {
    console.log('d', (new Date()) - start);
    // 4000ms sync process
    console.log('d', (new Date()) - start);
}

setTimeout(a1000, 6500);
setTimeout(b2000, 1000);
setTimeout(c3000, 6500);
setTimeout(d4000, 0);