function derp() { a(); b(); c(); } derp.toString() will return "function derp() { a(); b(); c(); }", but I only need the body of the function, so "a(); b(); c();", because I can then evaluate the expression. Is it possible to do this in a cross-browser way?
var entire = derp.toString(); var body = entire.slice(entire.indexOf("{") + 1, entire.lastIndexOf("}")); console.log(body); // "a(); b(); c();" Please use the search, this is duplicate of this question
.slice. It's the same, but less confusing.
var body = entire.slice(entire.indexOf("{") + 1, entire.lastIndexOf("}")); ?substring and substr generally confuse people. slice is a lot more memorable.
Since you want the text between the first { and last }:
derp.toString().replace(/^[^{]*{\s*/,'').replace(/\s*}[^}]*$/,''); Note that I broke the replacement down into to regexes instead of one regex covering the whole thing (.replace(/^[^{]*{\s*([\d\D]*)\s*}[^}]*$/,'$1')) because it's much less memory-intensive.
toString() instead of toString but this is the cleanest answer I've found, thank you !NOTE: The accepted answer depends on the interpreter not doing crazy things like throwing back comments between 'function' and '{'. IE8 will happily do this:
>>var x = function /* this is a counter-example { */ () {return "of the genre"}; >>x.toString(); "function /* this is a counter-example { */ () {return "of the genre"}" 
A single-line, short regex example:
var body = f.toString().match(/^[^{]+\{(.*?)\}$/)[1]; If you want to, eventually, eval the script, and assuming the function takes no parameters, this should be a tiny bit faster:
var body = '(' + f.toString() + ')()'; 
You need something like this:
var content = derp.toString(); var body = content.match(/{[\w\W]*}/); body = body.slice(1, body.length - 1); console.log(body); // a(); b(); c(); 
a(); b(); c();is not a valid expression though...;separates statements and hence cannot be part of an expression. Everything that throws a syntax error when put into the grouping operator(...)is not a valid expressions. But maybe the OP did not refer to this technical meaning with the term expression.