ChildNode.before() - Web APIs 编辑

The ChildNode.before() method inserts a set of Node or DOMString objects in the children list of this ChildNode's parent, just before this ChildNode. DOMString objects are inserted as equivalent Text nodes.

Syntax

[Throws, Unscopable]
void ChildNode.before((Node or DOMString)... nodes);

Parameters

nodes

A set of Node or DOMString objects to insert.

Exceptions

• HierarchyRequestError: Node cannot be inserted at the specified point in the hierarchy.

Examples

Inserting an element

var parent = document.createElement("div");
var child = document.createElement("p");
parent.appendChild(child);
var span = document.createElement("span");

child.before(span);

console.log(parent.outerHTML);
// "<div><span></span><p></p></div>"

Inserting text

var parent = document.createElement("div");
var child = document.createElement("p");
parent.appendChild(child);

child.before("Text");

console.log(parent.outerHTML);
// "<div>Text<p></p></div>"

Inserting an element and text

var parent = document.createElement("div");
var child = document.createElement("p");
parent.appendChild(child);
var span = document.createElement("span");

child.before(span, "Text");

console.log(parent.outerHTML);
// "<div><span></span>Text<p></p></div>"

ChildNode.before() is unscopable

The before() method is not scoped into the with statement. See Symbol.unscopables for more information.

with(node) {
  before("foo");
}
// ReferenceError: before is not defined 

Polyfill

You can polyfill the before() method in Internet Explorer 9 and higher with the following code:

// from: https://github.com/jserz/js_piece/blob/master/DOM/ChildNode/before()/before().md
(function (arr) {
  arr.forEach(function (item) {
    if (item.hasOwnProperty('before')) {
      return;
    }
    Object.defineProperty(item, 'before', {
      configurable: true,
      enumerable: true,
      writable: true,
      value: function before() {
        var argArr = Array.prototype.slice.call(arguments),
          docFrag = document.createDocumentFragment();

        argArr.forEach(function (argItem) {
          var isNode = argItem instanceof Node;
          docFrag.appendChild(isNode ? argItem : document.createTextNode(String(argItem)));
        });

        this.parentNode.insertBefore(docFrag, this);
      }
    });
  });
})([Element.prototype, CharacterData.prototype, DocumentType.prototype]);

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• ChildNode and ParentNode
• ChildNode.after()
• ParentNode.append()
• Node.appendChild()
• Node.insertBefore()
• Element.insertAdjacentElement()
• NodeList