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JavaScript provides you with three common ways to check if a property exists in an object: Use the hasOwnProperty() method. Use the in operator. Compare property with undefined .
Use the typeof() Function to Check Whether a Value Is an Object or Not in JavaScript. We can check the type of objects using the typeof() function.
The logical NOT ( ! ) operator (logical complement, negation) takes truth to falsity and vice versa. It is typically used with boolean (logical) values. When used with non-Boolean values, it returns false if its single operand can be converted to true ; otherwise, returns true .
There are mainly two methods to check the existence of a key in JavaScript Object. The first one is using “in operator” and the second one is using “hasOwnProperty() method”. Method 1: Using 'in' operator: The in operator returns a boolean value if the specified property is in the object.
It seems wrong to me to set up an if/else statement just to use the else portion...
Just negate your condition, and you'll get the else logic inside the if:
if (!(id in tutorTimes)) { ... }
As already said by Jordão, just negate it:
if (!(id in tutorTimes)) { ... }
Note: The above test if tutorTimes has a property with the name specified in id, anywhere in the prototype chain. For example "valueOf" in tutorTimes returns true because it is defined in Object.prototype.
If you want to test if a property doesn't exist in the current object, use hasOwnProperty:
if (!tutorTimes.hasOwnProperty(id)) { ... }
Or if you might have a key that is hasOwnPropery you can use this:
if (!Object.prototype.hasOwnProperty.call(tutorTimes,id)) { ... }
Personally I find
if (id in tutorTimes === false) { ... }
easier to read than
if (!(id in tutorTimes)) { ... }
but both will work.
Two quick possibilities:
if(!('foo' in myObj)) { ... }
or
if(myObj['foo'] === undefined) { ... }
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