Node.js script.runInNewContext() Method

The script.runInNewContext() method first contextifies the stated contextObject, runs the compiled code inside the vm.Script object within the context created and then returns the output. However, the running code has no access to the local scope.

Syntax:

script.runInNewContext( contextObject, options )

Parameters: This method accept two parameters as mentioned above and described below:

• contextObject: It is an object that will be contextified and if it is undefined, then a new object will be created,
• options: It is optional and returns Object.

  It holds the following parameters:

  
  
  
  1. displayErrors: It holds a Boolean value i.e. true if an error is thrown while compiling the code and the line of code because of which an error is thrown is linked to the stack trace. Its by default value is true.
  2. timeout: It holds an integer value that specifies the number of milliseconds taken in order to execute the stated code before ending the execution. However, if an execution is closed then an error will occur. And the value for this must be a positive integer absolutely.
  3. breakOnSigint: It holds a Boolean value. If its true, then the execution will be stopped as soon as SIGINT i.e, (Ctrl+C) is provided. And if the execution is stopped then an error is thrown. Its by default value is false.
  4. contextName: It holds a string. It is human readable names of the newly generated context. And by default it is ‘VM Context i’ where, i is the index of the generated context that is ascending numerically.
  5. contextOrigin: It holds a string. It is the origin that is equivalent to the recently generated context. Moreover, the origin must be formed like a URL. Its by default value is ”.
  6. contextCodeGeneration: It is of type Object.
     It holds the following parameters:
     • strings: It holds a Boolean value and if its set to false then any call to function constructors or eval will throw an error i.e, EvalError. Its default value is true.
     • wasm: It holds a Boolean value and if it is set to false then any tries to compile a WebAssembly module will throw an error i.e, WebAssembly.CompileError. Its by default value is true.

Return Value: It returns the result of the very last statement executed in the script.

Below examples illustrate the use of script.runInNewContext() method in Node.js:

Example 1:

// Node.js program to demonstrate the
// script.runInNewContext() method

// Including util and vm module
const util = require('util');
const vm = require('vm');

// Constructing context
const context = { x: 3, y:4 };

// Constructing a script
const script = new vm.Script('x *=11, y *=4;');


// Calling runInNewContext method
script.runInNewContext(context);

// Displays output
console.log("The output is: ", context);

Output:

The output is:  { x: 33, y: 16 }

Example 2:

// Node.js program to demonstrate the
// script.runInNewContext() method

// Including util and vm module
const util = require('util');
const vm = require('vm');

// Creating contexts
cont = {
      animal: 'dog',
      total_number: 5
    };

// Creating script with its parameters
var script = vm.createScript(
    'total_number += 5; name = "Sheru"', 'file.vm');

// Calling runInNewContext method
script.runInNewContext(cont);

// Displays output
console.log(cont);

Output:

{ animal: 'dog', total_number: 10, name: 'Sheru' }

Reference: https://nodejs.org/api/vm.html#vm_script_runinnewcontext_contextobject_options