By 06/07/2015 14 Comments

TypeScript Callback Function

Define Callback Function:

  • A callback function in TypeScript is a function which is passed from another function as its parameter.
  • A callback function is called automatically in another function when another/normal function is invoked/called explicitly.
  • A callback function is passed from a normal function as an argument in order to invoke it.


/* Following is a void type function which has an argument array as its parameter. This function is a callback function. */
function list(...products: string[]) {
    var pList: string[] = products;
    document.write("Product list: <br/>");

// loop through each element and print them
    for (var index = 0; index < pList.length; index++) {
        document.write( pList[index]);


/* Following is a function which has 2 parameters, 1st parameter is a callback function (callback) with its argument (...products: string[]) and its return type (void). 2nd parameter is an argument string type array.*/
function getList(callback: (...products: string[]) => void, ...pList: string[]) {

/* Following, a callback function is invoked/called and pass an array from it as an argument. */
        callback("" + pList);


/* Call a getList() function, this function passes 2 arguments, 1st is a callback function which is list() and 2nd arguments are multiple string values which is received by an argument array. */ 
getList(list, "Laptop", "Mobile phone", "Iron", "Television", "Table");


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