What is isDescendant() in dojo/dom?

Dojo is a JavaScript toolkit that provides many utility modules and functions to create a web application. We can save time and speed up the development process using the predefined Dojo modules. Dojo includes language utilities, UI components, and much more.

What is isDescendant() in dojo/dom?

The isDescendant method can be used to check if a DOM node is a descendant (child) of an ancestor (parent) node. In simple words, checks if a node is a child node of the given parent node. The isDescendant method is present in the dom module of the Dojo library.

Syntax

This method takes two arguments:

1. node: The node to be checked if it is a child element.

2. ancestorNode: The node inside which the child node availability is checked.

The argument type can be either string or a DOM node. If we pass a string then the string value is considered as the id of the element.

Return value

This method returns a boolean value. It will return true if the provided node argument (first argument) is a child element of the ancestorNode (second) argument, and false otherwise.

Example

Let's look at the code below:

Explanation

In the above code snippet:

• Lines 6–8: We have created a div element with an id value parent. We have added another div element inside the parent element with an id value child-1.

• Line 9: We have created a div element with an id value unknown-child .

• Line 11: We load the Dojo library from the CDN server.

• Line 13: We load the dojo/dom module that contains the isDescendant method.

• Line 14: We use the isDescendant method to check if the element with an id value child-1 is a child element of the element with an id value parent. For this method, we pass id strings as arguments. In our case, we have a child-1 element present inside the parent element so true is returned.

• Lines 18–19: We use the byId method to get the node element by providing the id string of the element. Using this method we get the element with id values parent and child-1 and assign it to the parent and child1 variables respectively.

• Line 21: We use the isDescendant method to check if the element child1 is a descendant(child) of the parent. For this method, we pass the DOM node as an argument. In our case, we have a child-1 element present inside the parent element so true is returned.

• Line 24: We use the isDescendant method to check if the element with id value unknown-child is a child element of the element with id value parent. For this method, we pass id strings as arguments. In our case, the unknown-child element is not the child element of the parent element so false is returned.