错误-预期分配或函数调用，而是看到一个表达式

Question

Im getting 2 errors in this for-loop. Both are giving me error:

Expected an assignment or function call and instead saw an expression.

The error is because of the two rows marked "//Here" below:

var f="";

var printRange =function(rangeStart,rangeStop){
    for (var a3=rangeStart; rangeStop>=a3; a3++) 
        rangeStop >=a3 && (f+=a3+",");                   //Here
        a3==rangeStop && (f+=a3);                    //Here
        return f.substr(0,f.length-1);
};

ANSWER = printRange(28,47);

I can't figure out why they are not correct. I can't see what I've done wrong.

Answer 1

Put the condition in an if block:

if (rangeStop >=a3) f += a3+",";  
if (a3==rangeStop) f += a3; 

Also, the for block is missing curly braces and the indentation is ambiguous so I'm not sure what you want/expect there. It's best to add them.