To allow form designers more flexibility and scripting power, LiveCycle Designer ES supports the use of JavaScript version 1.6 or earlier in all situations that support scripting.
Form developers familiar with JavaScript will be able to take their existing expertise and apply it directly to LiveCycle Designer ES. LiveCycle Designer ES provides a number of properties and methods that enhance JavaScript to allow you to access field and object values. These properties and methods combine with the LiveCycle Designer ES reference syntax to provide you with easy manipulation of form values and data.
Note:
The Script Editor does not provide syntax error checking for scripts created using JavaScript. In addition, statement completion options do not appear for standard JavaScript objects or methods.
See also 

About using JavaScript