I want to use an ES6 proxy to trap the following common code:  for (let key in trapped) {     if (!Object.prototype.hasOwnProperty.call(obj, key)) continue;     let value = trapped[key];     //various code }   But after reviewing the proxy documentat...
It seems to me that there are four different ways I can determine whether a given object (e.g. foo) has a given property (e.g. bar) defined:   if (foo.hasOwnProperty(bar)) { if ('bar' in foo) { if (typeof foo.bar !== 'undefined') { if...
I want to check if an input element is a checkbox or text type.  I know I can do this:  //Type of input.. if ( input.type === "checkbox" )  //Contains the property.. if ( "checked" in input )    But my question is: why do hasOwnProper...
hasOwnProperty seems to behave differently depending on whether it is called on a constructor function or an instance, depending on the use of this or let for the contained members.  function Animal(_name) {      let name = _name;      this.getName =...
Related to this question, i wanted to try out this  var arr = [0,1,2,true,4,{"abc":123},6,7,{"def":456},9,[10]]; arr.filter(Object.hasOwnProperty,"abc");//outputs [0, 1, 2] arr.filter(Object.hasOwnProperty,"2222222") /...
In JavaScript the in operator checks whether an object has the specified property. However, it doesn't check only object's own properties, but also the prototype chain. Therefore in some situations it may behave not exactly as expected.  Let&...
I've been having some trouble with the Free Code Camp lesson on checking if an object has certain properties.  In this lesson, we're supposed to use hasOwnProperty() to check if the users object contains Alan, Jeff, Sarah, and Ryan. If all of...
My understanding is that the Object.hasOwnProperty method checks if the object has a property name of it's own, meaning a non-inherited property. That would mean that the function should return false whenever the property a. doesn't exist, or...
Typically, the solution to for..in's notorious caveat is something along the lines of:  for(var prop in obj) {     if(obj.hasOwnProperty(prop)) {         foo(); bar(); baz();     } }   I feel like it would be cleaner to just do:  for(var prop in...

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