为什么这个箭头函数看起来与我所学的不同？[复制]

问：

我正在学习如何在 JS 中操作 DOM，并且对为什么传递给数组方法的箭头函数看起来如何感到困惑。在继续之前，我想先了解代码背后的逻辑。请查看代码中的 //。我已将该函数粘贴为普通函数和箭头函数，并将我的问题写在代码中。

const buttons = document.querySelectorAll('button');


buttons.forEach(function(button) { 
    button.addEventListener('click', function() {
        alert(button.id);
    });
});

buttons.forEach(button => { //why does 'function' not need to be declared here? 
    button.addEventListener('click', () => { // why does this need curly braces? Why can't the alert call stay on the same line? Also, I was taught that multiple line arrow functions must have 'return', but this clearly does not?
        alert(button.id);
    } );
    
});