jquery finds whether element exists

Jquery method to find whether an element exists: first create a front-end sample file; then pass "if($("#someID").length>0 ) {$("#someID").text(" hi");}" method can be used to determine whether the element exists.

The demonstration environment of this tutorial: windows7 system, jquery1.2.6 version, Dell G3 computer.

Recommended: jQuery video tutorial

jquery determines whether an element exists

In traditional Javascript Here, before we perform some operation on a page element, it is best to first determine whether the element exists. The reason is that operations on an element that does not exist are not allowed. For example:

document.getElementById("someID").innerText("hi");

If the element with the ID "someID" does not exist, we will get a Javascript run error: document.getElementById("someID") is null

The correct writing method should be:

obj = document.getElementById("someID");
if (obj){
  obj.innerText("hi");
}

So in jQuery, how do we determine whether a page element exists? If we refer to the traditional Javascript writing method above, the first way we think of must be:

if ($("#someID")){
  $("#someID").text("hi");
}

But this is wrong! Because jQuery objects always have a return value, $("someID") is always TRUE, and the IF statement does not play any judgment role. The correct way to write it should be:

if ( $("#someID").length > 0 ) {
$("#someID").text("hi");
}

Note: It is actually not necessary to judge whether a certain page element exists or not in jQuery. jQuery itself will ignore the operation of a non-existent element and will not report an error.

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