关于使用JavaScript调用函数，哪一个是正确的？

Question

I wrote a code in JavaScript shown below: in this code, onClick button wants to call function fadetext() , and the function fadetext() itself setTimeout.

 hex = 255 // Initial color value. function fadetext() { if (hex > 0) { //If color is not black yet hex -= 11; // increase color darkness document.getElementById("sample").style.color = "rgb(" + hex + "," + hex + "," + hex + ")"; setTimeout(fadetext, 20); } else hex = 255 //reset hex value } 

 <div id="sample" style="width:100%"> <h3>John slowly faded into view</h3> </div> <button onClick=fadetext()>Fade Text</button> 

However, when I refer to the answer, the differences are shown in the following two lines of codes:

setTimeout("fadetext()",20);

Another one is:

<button onClick="fadetext()">Fade Text</button>

Could somebody helps me to explain why this also works?

Answer 1

setTimeout takes a reference to a function that should be called when the timeout expires, not a string.

Although setTimeout can take a string that is eval d, do not use it , it's a security risk in the same way that eval() is.

setTimeout("fadetext()",20); should be setTimeout(fadetext,20);

and the onclick attribute is all lowercase.

<button onClick="fadetext()">Fade Text</button> should be <button onclick="fadetext()">Fade Text</button>

 var hex = 255 // Initial color value. function fadetext() { if (hex > 0) { //If color is not black yet hex -= 11; // increase color darkness document.getElementById("sample").style.color = "rgb(" + hex + "," + hex + "," + hex + ")"; setTimeout(fadetext, 20); } else hex = 255 //reset hex value } 

 <div id="sample" style="width:100%"> <h3>John slowly faded into view</h3> </div> <button onclick="fadetext()">Fade Text</button>