node/doc/api/script.markdown

Script

Script class compiles and runs JavaScript code. You can access this class with:

var Script = process.binding('evals').Script;

New JavaScript code can be compiled and run immediately or compiled, saved, and run later.

Script.runInThisContext(code, [filename])

Similar to process.compile. Script.runInThisContext compiles code as if it were loaded from filename, runs it and returns the result. Running code does not have access to local scope. filename is optional.

Example of using Script.runInThisContext and eval to run the same code:

var localVar = 123,
    usingscript, evaled,
    Script = process.binding('evals').Script;

usingscript = Script.runInThisContext('localVar = 1;',
  'myfile.js');
console.log('localVar: ' + localVar + ', usingscript: ' +
  usingscript);
evaled = eval('localVar = 1;');
console.log('localVar: ' + localVar + ', evaled: ' +
  evaled);

// localVar: 123, usingscript: 1
// localVar: 1, evaled: 1

Script.runInThisContext does not have access to the local scope, so localVar is unchanged. eval does have access to the local scope, so localVar is changed.

In case of syntax error in code, Script.runInThisContext emits the syntax error to stderr and throws.an exception.

Script.runInNewContext(code, [sandbox], [filename])

Script.runInNewContext compiles code to run in sandbox as if it were loaded from filename, then runs it and returns the result. Running code does not have access to local scope and the object sandbox will be used as the global object for code. sandbox and filename are optional.

Example: compile and execute code that increments a global variable and sets a new one. These globals are contained in the sandbox.

var util = require('util'),
    Script = process.binding('evals').Script,
    sandbox = {
      animal: 'cat',
      count: 2
    };

Script.runInNewContext(
  'count += 1; name = "kitty"', sandbox, 'myfile.js');
console.log(util.inspect(sandbox));

// { animal: 'cat', count: 3, name: 'kitty' }

Note that running untrusted code is a tricky business requiring great care. To prevent accidental global variable leakage, Script.runInNewContext is quite useful, but safely running untrusted code requires a separate process.

In case of syntax error in code, Script.runInThisContext emits the syntax error to stderr and throws an exception.

new Script(code, [filename])

new Script compiles code as if it were loaded from filename, but does not run it. Instead, it returns a Script object representing this compiled code. This script can be run later many times using methods below. The returned script is not bound to any global object. It is bound before each run, just for that run. filename is optional.

In case of syntax error in code, new Script emits the syntax error to stderr and throws an exception.

script.runInThisContext()

Similar to Script.runInThisContext (note capital 'S'), but now being a method of a precompiled Script object. script.runInThisContext runs the code of script and returns the result. Running code does not have access to local scope, but does have access to the global object (v8: in actual context).

Example of using script.runInThisContext to compile code once and run it multiple times:

var Script = process.binding('evals').Script,
    scriptObj, i;

globalVar = 0;

scriptObj = new Script('globalVar += 1', 'myfile.js');

for (i = 0; i < 1000 ; i += 1) {
  scriptObj.runInThisContext();
}

console.log(globalVar);

// 1000

script.runInNewContext([sandbox])

Similar to Script.runInNewContext (note capital 'S'), but now being a method of a precompiled Script object. script.runInNewContext runs the code of script with sandbox as the global object and returns the result. Running code does not have access to local scope. sandbox is optional.

Example: compile code that increments a global variable and sets one, then execute this code multiple times. These globals are contained in the sandbox.

var util = require('util'),
    Script = process.binding('evals').Script,
    scriptObj, i,
    sandbox = {
      animal: 'cat',
      count: 2
    };

scriptObj = new Script(
    'count += 1; name = "kitty"', 'myfile.js');

for (i = 0; i < 10 ; i += 1) {
  scriptObj.runInNewContext(sandbox);
}

console.log(util.inspect(sandbox));

// { animal: 'cat', count: 12, name: 'kitty' }

Note that running untrusted code is a tricky business requiring great care. To prevent accidental global variable leakage, script.runInNewContext is quite useful, but safely running untrusted code requires a separate process.