期望一个标识符，而不是看到一个表达式

Question

Hi,

I have this code:

obj = {"ignoredid":"3329"},{"ignoredid":"19693"};
hit = "3329";
if (Object.values(obj).indexOf(hit) > -1) {
   console.log('has it');
} else {console.log('doesnt');}

but I get a warning that says: expected an identifier and instead saw an expression

Why is that? This is the fiddle

https://jsfiddle.net/o7u5L90h/1/

the code works fine on the fiddle despite the warning but not on my actual project (there it will always output "doesnt" no matter what) so I wonder if it will work once I get rid of the warning. What am I missing here?

Thank you.

Answer 1

Maybe you want array of objects? Then you can do something like this

 // Helper function to check array of objects const hasIt = (obj, val) => { for(const v of obj) if(v['ignoredid'] === val) return true; return false; } // Define array of objects const obj = [{"ignoredid":"3329"},{"ignoredid":"19693"}]; // Test it if(hasIt(obj, "3329")) console.log('has it'); else console.log('doesnt');

Or with more recent approach

 // Define array of objects const obj = [{"ignoredid":"3329"},{"ignoredid":"19693"}]; // Test it if(obj.find(o => o.ignoredid === '3329')) console.log('has it'); else console.log('doesnt');

Answer 2

To answer your real question, what is happening there is that the statement obj = {ignoredid : 3329},{ignoredid : 19693}; does not cause a syntax error but does not do what you expect it to do.

Though it's not clear what you expected to happen 😁. That's why a lint is warning that expected an identifier and instead saw an expression

It's being interpreted as something close to the following:

 obj = {ignoredid : 3329}, {ignoredid : 19693}; console.log(JSON.stringify(obj)); // Is interpreted as obj = {ignoredid : 3329} {ignoredid : 19693} console.log(JSON.stringify(obj)); // Or ((obj = {ignoredid : 3329}), {ignoredid : 19693}); console.log(JSON.stringify(obj))

In both cases, the literal {ignoredid : 19693} is being discarded and not used by the program.

Note that if you started writing code that was using const/let or even var, you wouldn't have this problem and you'd be told you have a real syntax error and you wouldn't get this weird behavior. That is because a VariableDeclaration is not an Expression , and expressions separated by commas is what's happening here. See the end of the answer for further details.

Uncaught SyntaxError: Invalid destructuring assignment

 const obj = {ignoredid : 3329}, {ignoredid : 19693}; console.log(JSON.stringify(obj));

Explaining current behavior

If you intended it as obj = {ignoredid : 3329, ignoredid : 19693}; , that would mean that the obj would be {ignoredid : 19693} , that is, the last property with the same name wins out.

This is why you were always getting console.log('doesnt') , your object did not contain a value of 3329 only 19693 ;

Solution

As suggested by tark , Umitigate and me, you should use an array. I just wanted to answer the real question since the behavior is bit odd even outside of your quirky declaration😜

Gorier Technical details which explain the error message

If you analyze the syntax tree of your example , you'll notice that the body of the program is an ExpressionStatement but it does not contain an assignment directly, instead, it contains a nested SequenceExpression which contains a separate AssignmentExpression and an ObjectExpression which is not what you intended

However, if you analyze the syntax tree of obj = {"ignoredid":"3329"}; , you'll notice that there's an AssignmentExpression nested directly in the first ExpressionStatement of the program

So the message is indicating that it expected an Assignment but instead saw an Expression