javascript-objects | 易学教程

What makes a CanvasRenderingContext2D a CanvasRenderingContext2D?

阅读更多关于 What makes a CanvasRenderingContext2D a CanvasRenderingContext2D?

问题 Consider the following web page. <html> <body> <canvas id="canvas" width="300" height="300" style="border:1px solid #000000;"> </canvas> </body> </html> I open this page in Firefox, open the JS console and type the following. > document.getElementById("canvas").getContext("2d") The output is as follows: CanvasRenderingContext2D { canvas: canvas#canvas, mozCurrentTransform: (6) […], mozCurrentTransformInverse: (6) […], mozTextStyle: "10px sans-serif", mozImageSmoothingEnabled: true,

What makes a CanvasRenderingContext2D a CanvasRenderingContext2D?

阅读更多关于 What makes a CanvasRenderingContext2D a CanvasRenderingContext2D?

Filter array based on dynamic parameter

阅读更多关于 Filter array based on dynamic parameter

问题 Say I have an array of json objects which looks like below: var codes = [{ "code_id": "1", "code_name": "code 1", , }, { "code_id": "2", "code_name": "code889", }, // ... () ... ] How can I filter codes array based on dynamic input parameter? So I am looking for a generic function which will take input array and key and value as i/p. var filteredCodes = getFilteredCodes(codes, "code_id", 2); Thanks. 回答1: Use Array.prototype.filter to filter out the result - see demo below: var codes = [{"code

Convert flat list array to tree view array based on node number in Javascript

阅读更多关于 Convert flat list array to tree view array based on node number in Javascript

问题 I want to convert flat list array to tree view array based on node number in Javascript. Node number represent child array element. e.g. nodenumber 1.1 represent the children of element "A" and nodenumber 1.1.1 represent the children of element "B" and so on. input [ { "name": "A", "nodeNumber": "1" }, { "name": "B", "nodeNumber": "1.1" }, { "name": "C", "nodeNumber": "1.1.1" }, { "name": "D", "nodeNumber": "1.2" }, { "name": "E", "nodeNumber": "1.2.1" }, { "name": "F", "nodeNumber": "1.2.2"

object property to dynamically change with the value of assigned variable

阅读更多关于 object property to dynamically change with the value of assigned variable

问题 This may turn out to be a very basic question as I am a newbie. I am creating an object from a constructor. I want one of the properties of object to be linked to a variable. So if variable value changes, the property's value should also change. Example: I am working on kineticjs and am creating an object from constructor Rect . I want the value of the property draggable to dynamically change to the value of optvar whenever optvar changes. Var optvar="true"; rect = new Kinetic.Rect({ x: 22, y

In plain Javascript, trying to filter for multiple values in an array that contains User objects that contain other objects and arrays

阅读更多关于 In plain Javascript, trying to filter for multiple values in an array that contains User objects that contain other objects and arrays

问题 thanks for taking a look at this. Sorry for length, trying to be clear! WHAT I'M TRYING TO DO: I have an array of users (each user an object) and am trying to filter the users on multiple criteria ("males from France" OR "females from Spain and United States with Engineering skills" etc) but it's proven beyond my skills so far. The hard part has been that the users are objects within a User array, but within each user object, some values are additional objects or arrays. Here's what the user

How to combine two array of objects of different sizes, based on a property in Javascript?

阅读更多关于 How to combine two array of objects of different sizes, based on a property in Javascript?

问题 I have two arrays of objects that are different in length but share similar information. qrySearchLocID = [{ LocalLabID: '123f', SystemID: 5000152, AppLabID: 3 }, { LocalLabID: '12BC', SystemID: 5000384, AppLabID: 3 }, ]; and qrySearch = [{ sName: 'SomePlace1', lBusinessID: 37343, SystemID: 5000152 }, { sName: 'SomePlace2', lBusinessID: 39780, SystemID: 5000156 }, { sName: 'SomePlace3', lBusinessID: 50772, SystemID: 5000519 }, { sName: 'SomePlace4', lBusinessID: 31079, SystemID: 5000384 }, ]

Is there a nice way in javascript to removing Falsy values from a javascript object (not an array)?

阅读更多关于 Is there a nice way in javascript to removing Falsy values from a javascript object (not an array)?

问题 In JavaScript you have the nice .filter method to remove null or falsy values from arrays. So far I haven't been able to find a method to remove the same from JavaScript Objects. Why would this be? Currently you can create a function for arrays like : function stripNulls(arr) { return arr.filter(Boolean); } Is there a similar function that can be created for JS Objects, or is the way filter works not practical on JS Objects. 回答1: The answer to "can I do x to an object" (or an array for that

Is there a nice way in javascript to removing Falsy values from a javascript object (not an array)?

阅读更多关于 Is there a nice way in javascript to removing Falsy values from a javascript object (not an array)?

If babel converts let and const to var, what's the difference?

阅读更多关于 If babel converts let and const to var, what's the difference?

问题 I've tried the babel transpiler, and it converts All let, const and var to just var, so in all, what's the difference in our code usage? I have read documents and I know what's the difference between let, const and var , but if all of them are eventually converted to var , what's the difference ? it means that there shouldn't be any meaningful differences in performance or even scope! Update (02.14.2019) : Based on the answers I understood that scope does matter and even though they are