jQuery callbacks.has() 方法

The jQuery callbacks.has() method is used to determine whether a specific function exists among the currently registered callbacks.

Syntax

jQuery.Callbacks().has( function )

Parameters

function: The function to search for within the callback list.

Return Value

The has() method returns true if the specified function exists within the callback list, false otherwise.

Example

var callbacks = $.Callbacks();
  
function foo() {
  console.log('foo');
}

callbacks.add(foo);

console.log(callbacks.has(foo)); // output: true
console.log(callbacks.has(function() {})); // output: false

In the above example, a jQuery callback list is created using the jQuery.Callbacks() method. A function foo() is defined and added to the callback list using the add() method. The has() method is then called to check whether the foo() function exists within the list. Since foo() was added to the list, the has() method returns true. A new anonymous function is then created and passed to the has() method, but since this function was not added to the list, the has() method returns false.

Conclusion

The jQuery callbacks.has() method is a useful way to check whether a specific function exists within a jQuery callback list. It can be used to determine whether a function has been registered as a callback, allowing developers to take appropriate action if necessary.