HuasoFoundries / backgrid_es6

This checks looks for references to variables that have not been declared. This is most likey a typographical error or a variable has been renamed.

To learn more about declaring variables in Javascript, see the MDN.

The sequence or comma operator allows the inclusion of multiple expressions where only is permitted. The result of the sequence is the value of the last expression.

This operator is most often used in for statements.

Used in another places it can make code hard to read, especially when people do not realize it even exists as a seperate operator.

This check looks for usage of the sequence operator in locations where it is not necessary and could be replaced by a series of expressions or statements.

var a,b,c;

a = 1, b = 1,  c= 3;

could just as well be written as:

var a,b,c;

a = 1;
b = 1;
c = 3;

To learn more about the sequence operator, please refer to the MDN.

This check looks for parameters in functions that are not used in the function body and are not followed by other parameters which are used inside the function.

This check looks for parameters in functions that are not used in the function body and are not followed by other parameters which are used inside the function.

This check looks for functions where a return statement is found in some execution paths, but not in all.

Consider this little piece of code

function isBig(a) {
    if (a > 5000) {
        return "yes";
    }
}

console.log(isBig(5001)); //returns yes
console.log(isBig(42)); //returns undefined

The function isBig will only return a specific value when its parameter is bigger than 5000. In any other case, it will implicitly return undefined.

This behaviour may not be what you had intended. In any case, you can add a return undefined to the other execution path to make the return value explicit.

The loose comparison such as == or != might produce some weird results for some values, unless you explicitly want to have this behavior here, better use the strict alternative.

Learn more about loose comparison in Javascript.

Consider adding curly braces around all statements when they are executed conditionally. This is optional if there is only one statement, but leaving them out can lead to unexpected behaviour if another statement is added later.

Consider:

if (a > 0)
    b = 42;

If you or someone else later decides to put another statement in, only the first statement will be executed.

if (a > 0)
    console.log("a > 0");
    b = 42;

In this case the statement b = 42 will always be executed, while the logging statement will be executed conditionally.

if (a > 0) {
    console.log("a > 0");
    b = 42;
}

ensures that the proper code will be executed conditionally no matter how many statements are added or removed.