This client script will execute once forms are loaded.

I have explained the above pic in details in the video. Request you to watch it for better understanding.

Now lets take a look on real word example

Real World Scenario

Requirement: Hide “Closed” Incident state and State from everyone accept user who has itil_admin role.

Solution: create onload client script and write below code.

function onload() {
    if (g_user.hasrole('itil_admin'))
        return;

    if (g_form.getvalue('incident_state') != '7')
        g_form.removeoption('incident_state', 7);
    if (g_form.getvalue('state') != '7')
        g_form.removeoption('state', 7);
}

onChange client script will runs when a particular field value changes on the form.

I have explained the above pic in details in the video. Request you to watch it for better understanding.

In onChange() client script we will get below OOB parameters/Objects. Let me explain you each object in details.

A. control: the DHTML (Dynamic Hyper Text Markup Language) widget whose value changed.

• • • Control parameters are generally used for If we wants to change the dynamically field size, length etc. in ui page. So we will use control parameter inside client script in onChange type. 
    • It’s basically the field for which this client script is written. And it will give you HTML objectfor that field so that you can change or use it as per your need for example restricting field length.
    • Name of the object (field_name) whose value just changed. The object is identified in the Field name field on the Client Script form.
    • To change the field value color we can use this script: style.color = ‘blue’;

 Note: control is not accessible in mobile and service portal. 

B. oldVaIue— Value of the control field when the form loaded and prior to the change. For example, if the value of Assigned to changes from Runjay to Suman, the value of the parameter oldValue is Runjay. oldVaIue will always be Runjay (the value when the form loaded) no matter how many times the Assigned to value changes after the original form load.

C. newVaIue— Value of the control field after the change. For example, if the value of Assigned to changes from Runjay to Suman, the value of the parameter newValue will be Suman.

D. isLoading— Boolean value indicating whether the change is occurring as part of a form load. Value is true if change is due to a form load. A form load means all of a form’s fields changed.

E. isTemplate— Boolean value indicating whether the change occurred due to population of the field by a template. Value is true if change is due to population from a template.

Now lets take a look on real word example

Real World Scenario

Requirement: Make Assignment group and assigned to field mandatory if state changes from New to In-Progress.

Solution: create onChange client script and write below code.

function onChange(control, oldValue, newValue, isLoading, isTemplate) {
   if (isLoading || newValue === '') {
      return;
   }
    if(newValue == 2){
        g_form.setMandatory('assignment_group', true);
        g_form.setMandatory('assigned_to', true);
    }else{
        g_form.setMandatory('assignment_group', false);
        g_form.setMandatory('assigned_to', false);
    }
   
}	

This type of client script runs when a form is submitted.  It is used to validate things on the form and ensure that the submission makes sense. An onSubmit() client script can cancel form submission by returning a value of false.

• • Script runs when a form is saved, updated, or submitted
  • Typically used for field validation

I have explained the above pic in details in the video. Request you to watch it for better understanding.

Now lets take a look on real word example

Real World Scenario

Requirement: If IT fulfiller clicks on Cancel button then make Cancel Reason field mandatory with alert / error stating cancel reason field is mandatory.

Solution: create onSubmit client script and write below code.

function onSubmit() {
   if(g_form.getValue('state') ==8 && g_form.getValue('u_cancel_reason') ==''){
       
       g_form.addErrorMessage('Reason field is mandatory !!');
       return false;
   }
}

This type of client script runs when the list editor changes a cell value. Script runs when a particular field value on a list changes. Applies to all records selected.

In onCellEdit() client script we will get OOB parameters/Objects. Let me explain you each object in details.

Request you to watch it for better understanding.

A. sysIDs: It consist an array of the sys_ids for all items being edited.

B. table: The table of the items being edited.

C. oldValues: The old values of the cells being edited.

D. newValue: The new value for the cells being edited.

E. callback: A callback that continues the execution of any other related cell edit scripts.

If true is passed as a parameter, the other scripts are executed or the change is committed if there are no more scripts. If false is passed as a parameter, any further scripts are not executed and the change is not committed.

Now lets take a look on real word example

Real World Scenario

Requirement: Prevent state being edited from list view of incident if state marked as Resolved or Closed.

Solution: create onCellEdit client script and write below code.

function onCellEdit(sysIDs, table, oldValues, newValue, callback){
var saveAndClose = true;

if(newValue == 6) { //Resolved
alert("You cannot change the State to 'Resolved' from a list");
saveAndClose = false;
}
if(newValue == 7) { //Closed
alert("You cannot change the State to 'Closed' from a list");
saveAndClose = false;
}
callback(saveAndClose);
}