JavaScript Key существует
var person={"name":"Billy","age":20}
person.hasOwnProperty("name"); // true
person.hasOwnProperty("sex"); // false
Grepper
var person={"name":"Billy","age":20}
person.hasOwnProperty("name"); // true
person.hasOwnProperty("sex"); // falseif (obj.hasOwnProperty("key1")) {
...
}"key" in obj // true, regardless of the actual value
If you want to check if a key doesn't exist, remember to use parenthesis:
!("key" in obj) // true if "key" doesn't exist in object
!"key" in obj // ERROR! Equivalent to "false in obj"
Or, if you want to particularly test for properties of the object instance (and not inherited properties), use hasOwnProperty:
obj.hasOwnProperty("key") // true"key" in obj // true, regardless of the actual value!("key" in obj) // true if "key" doesn't exist in object
!"key" in obj // ERROR! Equivalent to "false in obj"
5003
Checking for undefined-ness is not an accurate way of testing whether a key exists. What if the key exists but the value is actually undefined?
var obj = { key: undefined };
console.log(obj["key"] !== undefined); // false, but the key exists!