definedButNotInitialized in window: true definedAndInitialized in window: false someObject.firstProp in window: false someObject.secondProp in window: false …

Dec 31, 2009 · In JavaScript, the following values will cause the if condition to fail and not execute its statement: null, undefined, false, NaN, the number 0, and the empty string ''. Assuming that …

Aug 22, 2021 · undefined: A variable that has not been assigned a value is of type undefined. A method or statement also returns undefined if the variable that is being evaluated does not …

Jan 30, 2021 · You are getting undefined because the Greeter-object is indeed undefined. This is a more detailed explanation of all the parts: This is a more detailed explanation of all the parts:

Jul 27, 2016 · As I can see in almost case, javascript would throw message undefined or x is not defined, etc... Here is some: var i; var j = i; alert(j); // undefined var xyz; alert(xyz); // undefined …

Jan 18, 2012 · If it undefined, then the rest of the expression is moot, so we won’t even bother to evaluate it. AND if it is defined, then let’s check for the existence of some property that we’re …

May 30, 2017 · At present, I think the best answer is to use either Flow or Typescript to enforce static type safety. These options weren’t really available when I wrote the original answer, but …

Apr 22, 2009 · undefined === undefined // true null == undefined // true null === undefined // false The object.x === undefined should return true if x is unknown property. In chapter Bad Parts of …

Mar 3, 2017 · Sorry for necromancing, but most of the answers here confuse 'undefined' and 'not defined' Undefined - a variable is declared but it's value is undefined. Not defined - a variable …

Dec 16, 2013 · You're not calling changeCheckBox anywhere in your code thus, the op is never set. Maybe you meant to have onchange="changeCheckBox(this.value);" for every check box …