Javascript: AppendChild_问答_开发者_运维开发者技术经验分享

I was learning about appendChild and have so far come up with this code:

var blah = "Blah!";
var t = document.createElement("table"),
  tb = document.createElement("tbody"),
  tr = document.createElement("tr"),
  td = document.createElement("td");

t.style.width = "100%";
t.style.bord开发者_运维百科erCollapse = 'collapse';

td.appendChild(document.createTextNode(blah));

// note the reverse order of adding child        
tr.appendChild(td);
tb.appendChild(tr);
t.appendChild(tb);

document.getElementById("theBlah").appendChild(t);

<div id="theBlah">d</div>

But that gives me an error saying Uncaught TypeError: Cannot call method 'appendChild' of null. What am I doing wrong?

Try wrapping your JavaScript in an onload function. So first add:

<body onload="load()">

Then put your javascript in the load function, so:

function load() {
    var blah="Blah!";
    var t  = document.createElement("table"),
    tb = document.createElement("tbody"),
    tr = document.createElement("tr"),
    td = document.createElement("td");

    t.style.width = "100%";
    t.style.borderCollapse = 'collapse';

    td.appendChild(document.createTextNode(blah)); 

    // note the reverse order of adding child        
    tr.appendChild(td);
    tb.appendChild(tr);
    t.appendChild(tb);

   document.getElementById("theBlah").appendChild(t);
}

The script is being run before the page completes loading. Which is why document.getElementById("theBlah") returns null.

Either use something like jQuery or simply something like

<script>
window.onload = function () {
    var blah="Blah!";
    var t  = document.createElement("table"),
    tb = document.createElement("tbody"),
    ...
    //the rest of your code here
};
</script>

The problem is that document.getElementById("theBlah") returns null. The reason why is that your code is running before the theBlah element has been created. You should place your code in an onload event handler.

proper way (rows & cols & the random innerText is set dynamically ...by you) this way is probably not the shortest but by way the fastest to build a table. It’s also a full table with thead and filled with random text:

use native JavaScript (not slowing down JQuery)
(function(){})() executes the code before body is loading
doesn’t have problems with other variables outside the function
and pass the document so you have shorter variables
there is a way to shorten the function by using clone node... but it’s slower and maybe not supported by all browsers
use createDocumentFragment() to create the tr’s. If you have a lot of rows this helps to build the DOM faster.

    (function (d) {
        var rows = 10,
            cols = 3,
            t = d.createElement('table'),
            the = d.createElement('thead'),
            tb = d.createElement('tbody'),
            tr = d.createElement('tr');
        t.style.width = "100%";
        t.style.borderCollapse = 'collapse';
        for (var a = 0; a < cols; a++) {
            var th = d.createElement('th');
            th.innerText = Math.round(Math.random() * 100);
            tr.appendChild(th);
        };
        the.appendChild(tr);
        var f = d.createDocumentFragment();
        for (var a = 0; a < rows; a++) {
            var tr = d.createElement('tr');
            for (var b = 0; b < cols; b++) {
                var td = d.createElement('td');
                td.innerText = Math.round(Math.random() * 100);
                tr.appendChild(td);
            }
            f.appendChild(tr);
        }
        tb.appendChild(f);
        t.appendChild(the);
        t.appendChild(tb);
        window.onload = function () {
            d.body.appendChild(t)
        };
    })(document)

I believe you can just link your JavaScript to your html using the defer attribute.

<script src="script.js" defer></script>

This way your JavaScript will not run until after the page has loaded.

Do yourself and us a favor and use JQuery. Everything becomes much simpler.

$('div.SomeDiv').append($('<table></table>').css('width','100%').append($('<tbody></tbody>').append($('<tr></tr>').append($('<td></td>').html("Blah Text"))))); // Everything else you want to add here...