如何在动态字符串上使用javascripts replace（）

Question

Working with a expression i got from an api source code. Can't get it to work how they have it. Or, it is not working how I would expect.

//original expression
// returns an anonymous function signature for example 'function(a, b)'
var args = ['a', 'b', 'c'];
    return 'function ' + (args[1] || '').replace('/[\s\r\n]+/', ' ');

//1 - this works
var args = ['a', 'b', 'c'];

var string1 = 'function ' + (args[1] || '');
console.log(string1.replace(/function/, 'fn'));    
// fn b

//2- this.does not(using the api's expression construct)
console.log('function' + (args[1] || '').replace(/function/, 'fn'));  
// function b

Question: Why is the replace not working in the #2? looking to get 'fn b' as a result in the one expression. myplunk thx

Answer 1

You are running the replacement on the string before you add "function" to it:

(args[1] || '').replace(/function/, 'fn')

You need to add more parens.

('function' + (args[1] || '')).replace(/function/, 'fn')