JS indexof() always returns -1

Problem description ：

Use indexOf() Determine whether a value is in Js in . When you try , This number is just js Array , But always return -1.

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Cause analysis ：

Consider whether the type is correct .

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Solution ：

Number( Numeric variable );
for example ：
var idCar = ‘3’;
var value = indexOf(idCar);
console.log(value);
if(value != -1){
alert(“ The ID card already exists ”);
}