I have some objects with properties. I wanted to test to see if they had characters in them so I initially wrote this:
if (MyObject.Prop1.length > 0) {....}
However, sometimes the object may not have a certain property so I was getting the error "cannot get length".
I changed it by writing this:
if (MyObject.Prop1 && MyObject.Prop1.length > 0) {....}
I'm using the chrome inspector and when I run the code, I don't get the error anymore. Is this going to work in every browser?
Thanks.
As an alternative:
if ('Prop1' in MyObject && MyObject.Prop1.length > 0) { ... )
Or, to be even more careful:
if (MyObject.hasOwnProperty('Prop1') && MyObject.Prop1.length > 0) { ... }
Of course that might be the wrong thing to do, depending on the nature of "MyObject".
Yes it will work quite fine, although you can save yourself the > 0 and just do
if (MyObject.Prop1 && MyObject.Prop1.length) {....}
since anything other than zero will evaluate to true.
Since undefined, 0, and "" are all "falsy" in JavaScript, this is equivalent:
if(MyObject.Prop1) {
// ...
}
Rick Waldron's "Idiomatic JavaScript" is a good reference for simplifying conditional statements without sacrificing correctness. You can test its use yourself:
function testProp(val) {
if(val) {
return val.length;
}
return "nope!";
}
var myObj = { stringProp : "foo",
emptyStrProp : "",
// undefinedProp is not defined
zeroProp : 0,
twelveProp : 12,
otherObjProp : document.createElement('div'),
arrayProp : [ 'a', 'b' ]
};
console.log( testProp( myObj.stringProp ) ); // => 3
console.log( testProp( myObj.emptyStrProp ) ); // => "nope!"
console.log( testProp( myObj.undefinedProp ) ); // => "nope!"
// of course if you're expecting values other than strings and undefined
// you'll have to account for them
console.log( testProp( myObj.zeroProp ) ); // => "nope!"
console.log( testProp( myObj.twelveProp ) ); // => undefined
console.log( testProp( myObj.otherObjProp ) ); // => undefined
console.log( testProp( myObj.arrayProp ) ); // => 2
0 is "falsy" and all other numbers are "truthy," so if prop === 0 then if(prop) will evaluate it as false, and if prop == 1 or 5 or -10 or 3.333 then if(prop) will come up true. If you evaluate prop.length where prop is equal to anything without a length property (including numbers), though, you will get undefined, which is falsy. I hope that's helpful.
Prop1will always be a string? Because now, if it contains the Number0, your condition will befalse. And numbers don't have a length property also.