In angular.js , Is function call without () different from call with()?

Question

I write some example code about $timeout service.

var myModule = angular.module('timerTest',[]);


        myModule.controller('counting',function($scope,$timeout)
        {
            var timerObject;
            var count =0;

            var countTime = function()
            {
                count++;
                console.log(count);
                $scope.value = count;
                timerObject = $timeout(countTime,1000);
            };

            $scope.startTimer = function()
            {
                console.log('timer start!');
                $timeout(countTime,1000);
            };

            $scope.endTimer = function()
            {
                console.log('End Timer');
                $timeout.cancel(timerObject);
            };

        });

In that code at countTime function, when I wrote

timerObject = > $timeout(countTime(),1000);

It calls countTime() very fast so It will make callstack overflow.
But when I wrote

timerObject = $timeout(countTime,1000);

It works perfectly. Is any different from that?

Joe Clay · Accepted Answer · 2016-03-12 13:07:32Z

2

timerObject = $timeout(countTime(),1000) immediately calls countTime on that line, and passing the result of this into $timeout. Whenever you put parentheses after a function name, it means you're calling the function right there and then - since you're doing this in every iteration of your function, it's causing it to endlessly repeat, hence the stack overflow.

timerObject = $timeout(countTime,1000), on the other hand, passes the countTime function itself into $timeout - this is the correct way to use the service, and will cause $timeout to call countTime after approximately 1000 milliseconds.

answered Mar 12, 2016 at 13:07

Joe Clay

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2 Comments

Jaeyoung Lee Over a year ago

Thank you for perfectly answer!

Joe Clay Over a year ago

@JaeyoungLee - Glad I could help! I feel like this trips people up pretty often.

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