Helper in Lightning Bundle

Helper in lightning bundle is similar to controller where you write client-side javascript methods. These methods are more like reuseable methods which can be called from any controller method.

• Helper is similar to controller but helper does not handle events.
• Helper can be used to write reusable Javascript methods and these can be called from Controller section.
• Helper functions also enable specialization of tasks, such as processing data and queueing server-side actions.
• Helper methods are local to Component bundle.
• Helper methods can be called from any controller javascript methods.
• Declaring a helper method is similar to controller javascript method.
• A helper function can pass in any arguments required by the function, such as the component it belongs to, a callback, or any other objects.
• You can call a helper method from another helper method using this. operation.

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Example:

({
    helperMethod1 : function() {
        // logic here
    },

    helperMethod2 : function(component) {
        // logic here
        this.helperMethod3(var1, var2);
    },

     helperMethod3 : function(var1, var2) {
         // do something with var1 and var2 here
    }
})

If you observe, helperMethod2 is calling helperMethod3 function as this.helperMethod3().

How can you call a helper method from controller?

If you see controller section which has 3 parameters, component, event, helper. Using helper component reference you can call a helper method.

If reference is helper, then

helper.helperMethod1();
helper.helperMethod2(component);
helper.helperMethod3(var1,var2);

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Note:

A helper is in lightning bundle is saved as componentNameHelper.js. If you component name is My_Lightning_Component, then a controller will be saved as My_Lightning_ComponentHelper.js.