Tuesday 30 April 2024

What is the purpose of the “do” keyword in dataweave?326

 What is the purpose of the “do” keyword in dataweave? 

In DataWeave, the do keyword serves the purpose of creating a local scope within your DataWeave script. This local scope allows you to define variables and functions that are only accessible within that specific block of code, promoting better organization and avoiding naming conflicts.

Here's a closer look at how the do keyword functions in DataWeave:

Local vs. Global Scope:

  • DataWeave scripts can have both global variables and local variables.

  • Global variables are defined in the header section of the script and are accessible throughout the entire script.

  • Local variables are defined within a do scope and are only accessible within that specific block.

Benefits of Using do for Local Scope:

  • Reduced Naming Conflicts: By using local variables, you can avoid potential conflicts with identically named variables defined elsewhere in the script or even globally. This improves code readability and maintainability.

  • Improved Code Organization: Local scopes with do help structure your code by grouping related variables and functions together, making the script easier to understand and modify.

  • Data Encapsulation: Local variables promote data encapsulation by limiting their accessibility to a specific code block. This can enhance data security and prevent unintended modifications.


do {
  -- Local variable definitions and function implementations here
} ---

  • The do keyword initiates the local scope.

  • Variable definitions and function implementations can be placed within the curly braces {}.

  • The triple dash --- (three hyphens) serves as a separator, signifying the end of the local scope. Any code after the separator can access variables and functions defined outside the do block.


%dw 2.0
output application/json

var globalName = "Global Variable"

do {
  var localName = "Local Variable"
  fun localFunction(param) = param * 2
} ---

  "global": globalName,
  "local": localFunction(5) // This will work as localFunction is accessible within the scope
  // "local": localName  // This would cause an error as localName is not accessible here

In this example:

  • globalName is a global variable accessible throughout the script.

  • The do block creates a local scope.

  • localName is a local variable defined within the scope and cannot be accessed outside of it.

  • localFunction is a local function defined within the scope.

  • The output object can access the global variable globalName.

  • It can also call the localFunction because it's defined within the same scope.

  • However, attempting to access localName directly outside the do block would result in an error as it's not in scope.


The do keyword along with local scopes is a valuable tool for organizing your DataWeave code, enhancing readability, and preventing naming conflicts within your MuleSoft applications.

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