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javascriptevalstring-parsing

Trying to understand output from JavaScript eval which does String parsing

Can anyone explain me why the following Java code which executes the JavaScript return "Smith" here? 

    ScriptEngineManager manager = new ScriptEngineManager();
    ScriptEngine engine = manager.getEngineByName("js");
    String jsSnippet = "var fullName = 'Joe Smith'; fullName.substring(fullName.indexOf(' ') + 1);";
    System.out.println(engine.eval(jsSnippet));

Similar JavaScript code (jsFiddle) which gives the same output as above Java code is

var jsSnippet = "var fullName = 'Joe Smith'; fullName.substring(fullName.indexOf(' ') + 1);";
document.write(eval(jsSnippet));

PS: I know eval is evil, but this is one of the circumstances I have to use JavaScript eval.

Solution

  • The eval function evaluates the last expression passed into it, and returns its value. See the relevant section on eval at the Mozilla Developer Network.