Develop Reference

Loop Inside function of React Component

(React web app development)
In order to check if the current stock status of products, I use ID of products to loop through json data.
I am trying to retrieve value of "DATAPAYLOAD" by key (id) from json (below). idsent is string passed from another component. But "if (Data.response[i].id === idsent)" this condition always appears to be false because I got "failed" in console.
That would be really helpful if someone could take a look at the following code and give me some sujections, thanks in advance!
onButtonClicked = () => {
const idsent="D56F36C6038DFC8244F"
for (var i = 0; i < Data.response.length; i++) {
if (Data.response[i].id === idsent) {
name = Data.response[i].DATAPAYLOAD;
const word = '<INSTOCKVALUE>INSTOCK</INSTOCKVALUE>';
if (name.includes(word)) {
return true;
}
else {
return false;
}
}
console.log("failed");
}
The following is part of the json data that is requested through fetch get-method.
Data= {
"code": 200,
"response": [
{
"id": "CED62C6F96BD0E21655142F",
"DATAPAYLOAD": "<AVAILABILITY>\n <CODE>200</CODE>\n
<INSTOCKVALUE>OUTOFSTOCK</INSTOCKVALUE>\n</AVAILABILITY>"
},
{
"id": "D56F36C6038DFC8244F",
"DATAPAYLOAD": "<AVAILABILITY>\n <CODE>200</CODE>\n
<INSTOCKVALUE>LESSTHAN10</INSTOCKVALUE>\n</AVAILABILITY>"
},
{
"id": "4536C9E608B563A749",
"DATAPAYLOAD": "<AVAILABILITY>\n <CODE>200</CODE>\n
<INSTOCKVALUE>INSTOCK</INSTOCKVALUE>\n</AVAILABILITY>"
},
{
"id": "3A576872130625CABFADEE68",
"DATAPAYLOAD": "<AVAILABILITY>\n <CODE>200</CODE>\n
<INSTOCKVALUE>INSTOCK</INSTOCKVALUE>\n</AVAILABILITY>"
}
]
}
Thank you again.

You probably wanted console.log("failed"); outside of the for loop like the following (so that it only executes once all the data is processed):
onButtonClicked = () => {
const idsent="D56F36C6038DFC8244F"
for (var i = 0; i < Data.response.length; i++) {
if (Data.response[i].id === idsent) {
name = Data.response[i].DATAPAYLOAD;
const word = '<INSTOCKVALUE>INSTOCK</INSTOCKVALUE>';
if (name.includes(word)) {
return true;
}
else {
return false;
}
}
}
console.log("failed");

When the fetch is successful, You need to read and parse the data using json(). Pleas read this
onButtonClicked = async () => {
const idsent="D56F36C6038DFC8244F"
Data = await Data.json(); // json() will create a promise
for (var i = 0; i < Data.response.length; i++) {
if (Data.response[i].id === idsent) {
name = Data.response[i].DATAPAYLOAD;
const word = '<INSTOCKVALUE>INSTOCK</INSTOCKVALUE>';
if (name.includes(word)) {
return true;
}
else {
return false;
}
}
console.log("failed");
}

The reason you get failed, is because the first time through, the ID does not match the one sent, so it console logs the "failed" message. Then the second time through the for loop it matches the data, and then hits the next if, which checks for the value. Since the value you are searching for is included in the data, it returns true and the for loop is exited. The reason you see the fail log is because you are logging when the id doesn't match and there are 3 records in that array where the id don't match, the first one being one of them.

React object property assignment only works the first time

For the following code, parameters are js objects whose structures are initialized as follows:
statePiece = {
field_name: { disabled: false, exampleValue: "arbitrary" },
field_name2: {
/* ... */
},
field_nameN: {
/* ... */
}
};
userField = "field_name_string";
sesarValues = {
format: "one2one",
selectedField: "latitude",
disabledSelf: true,
addField: 0
};
This function works correctly and returns the modified statePiece as returnTemp the first time a particular statePiece.field_name is modified
export let setUserField = (statePiece, userField, sesarValues) => {
console.log("set user field", userField, "set mappval", sesarValues);
var temp = { ...statePiece }; //(this.state.fields[each].mappedTo != null) ? (this.state.fields[userField].mappedTo) : [];
var XUnit = statePiece[userField];
if (typeof userField != "string") {
console.log("not string");
for (var each of userField) {
if (sesarValues) {
temp[each].mappedTo = sesarValues.selectedField;
temp[each].disabled = true;
} else {
temp[each].disabled = !temp[each].disabled;
delete temp[each].mappedTo;
}
}
} else {
//is string
console.log("is string");
console.log(XUnit);
if (sesarValues) {
if (XUnit.disabled === true) XUnit.disabled = false;
console.log("1");
console.log(XUnit);
XUnit.disabled = true;
console.log(XUnit);
XUnit.mappedTo = sesarValues.selectedField;
} else {
console.log("2");
temp[userField].disabled = !temp[userField].disabled;
delete temp[userField].mappedTo;
}
}
let returnTemp = { ...temp, [userField]: XUnit };
console.log("set UF debug ", returnTemp);
console.log(returnTemp["FACILITY_CODE"]);
return returnTemp;
};
But after that, changing the statePiece.userField.mappedTo value fails to alter the object property. Or at least alter it permanently. When I console log the returnTemp variable, I see the entry has lost its mappedTo entry(as should happen) without it being replaced with the new userField.
However, when I console.log(returnTemp[userField]) it shows the entry values with the expected mappedTo key: value pair.
Not sure what's going on here.

From the usage of userField, I can work out that it could be an Array or a String.
However you have done something curious with it in the following expression:
var XUnit = statePiece[userField];
Given userField is a String, the above expression is fine.
However, where it is an array, XUnit will be undefined.
Also doing the same where userField is an Array in the following line means that you're setting the userField.toString() as a key mapped to undefined.
let returnTemp = { ...temp, [userField]: XUnit };
I'd assign XUnit where the condition checks out that userField is a String and just return temp.
else {
//is string
var XUnit = statePiece[userField];
//...
}
return temp;

Trying to convert existing synchronous XmlHttpRequest object to be asynchronous to keep up with current fads

Soo, I keep getting slammed with cautions from Chrome about how synchronous XmlHttpRequest calls are being deprecated, and I've decided to have a go at trying to convert my use-case over in order to keep up with this fad...
In this case, I have an ~9 year old JS object that has been used as the central (and exemplary) means of transporting data between the server and our web-based applications using synchronous XHR calls. I've created a chopped-down version to post here (by gutting out a lot of sanity, safety and syntax checking):
function GlobalData()
{
this.protocol = "https://";
this.adminPHP = "DataMgmt.php";
this.ajax = false;
this.sessionId = "123456789AB";
this.validSession = true;
this.baseLocation = "http://www.example.com/";
this.loadResult = null;
this.AjaxPrep = function()
{
this.ajax = false;
if (window.XMLHttpRequest) {
try { this.ajax = new XMLHttpRequest(); } catch(e) { this.ajax = false; } }
}
this.FetchData = function (strUrl)
{
if ((typeof strURL=='string') && (strURL.length > 0))
{
if (this.ajax === false)
{
this.AjaxPrep();
if (this.ajax === false) { alert('Unable to initialise AJAX!'); return ""; }
}
strURL = strURL.replace("http://",this.protocol); // We'll only ask for data from secure (encrypted-channel) locations...
if (strURL.indexOf(this.protocol) < 0) strURL = this.protocol + this.adminPHP + strURL;
strURL += ((strURL.indexOf('?')>= 0) ? '&' : '?') + 'dynamicdata=' + Math.floor(Math.random() * this.sessionId);
if (this.validSession) strURL += "&sessionId=" + this.sessionId;
this.ajax.open("GET", strURL, false);
this.ajax.send();
if (this.ajax.status==200) strResult = this.ajax.responseText;
else alert("There was an error attempting to communicate with the server!\r\n\r\n(" + this.ajax.status + ") " + strURL);
if (strResult == "result = \"No valid Session information was provided.\";")
{
alert('Your session is no longer valid!');
window.location.href = this.baseLocation;
}
}
else console.log('Invalid data was passed to the Global.FetchData() function. [Ajax.obj.js line 62]');
return strResult;
}
this.LoadData = function(strURL)
{
var s = this.FetchData(strURL);
if ((s.length>0) && (s.indexOf('unction adminPHP()')>0))
{
try
{
s += "\r\nGlobal.loadResult = new adminPHP();";
eval(s);
if ((typeof Global.loadResult=='object') && (typeof Global.loadResult.get=='function')) return Global.loadResult;
} catch(e) { Global.Log("[AjaxObj.js] Error on Line 112: " + e.message); }
}
if ( (typeof s=='string') && (s.trim().length<4) )
s = new (function() { this.rowCount = function() { return -1; }; this.success = false; });
return s;
}
}
var Global = new GlobalData();
This "Global" object is referenced literally hundreds of times across 10's of thousands of lines code as so:
// Sample data request...
var myData = Global.LoadData("?fn=fetchCustomerData&sortByFields=lastName,firstName&sortOrder=asc");
if ((myData.success && (myData.rowCount()>0))
{
// Do Stuff...
// (typically build and populate a form, input control
// or table with the data)
}
The server side API is designed to handle all of the myriad kinds of requests encountered, and, in each case, to perform whatever magic is necessary to return the data sought by the calling function. A sample of the plain-text response to a query follows (the API turns the result(s) from any SQL query into this format automatically; adjusting the fields and data to reflect the retrieved data on the fly; the sample data below has been anonymized;):
/* Sample return result (plain text) from server:
function adminPHP()
{
var base = new DataInterchangeBase();
this.success = true;
this.colName = function(idNo) { return base.colName(idNo); }
this.addRow = function(arrRow) { base.addRow(arrRow); }
this.get = function(cellId,rowId) { return base.getByAbsPos(cellId,rowId); }
this.getById = function(cellId,rowId) { return base.getByIdVal(cellId,rowId); }
this.colExists = function(colName) { return ((typeof colName=='string') && (colName.length>0)) ? base.findCellId(colName) : -1; }
base.addCols( [ 'id','email','firstName','lastName','namePrefix','nameSuffix','phoneNbr','companyName' ] );
this.id = function(rowId) { return base.getByAbsPos(0,rowId); }
this.email = function(rowId) { return base.getByAbsPos(1,rowId); }
this.firstName = function(rowId) { return base.getByAbsPos(2,rowId); }
this.lastName = function(rowId) { return base.getByAbsPos(3,rowId); }
this.longName = function(rowId) { return base.getByAbsPos(5,rowId); }
this.namePrefix = function(rowId) { return base.getByAbsPos(6,rowId); }
this.nameSuffix = function(rowId) { return base.getByAbsPos(7,rowId); }
this.companyName = function(rowId) { return base.getByAbsPos(13,rowId); }
base.addRow( [ "2","biff#nexuscons.com","biff","broccoli","Mr.","PhD","5557891234","Nexus Consulting",null ] );
base.addRow( [ "15","happy#daysrhere.uk","joseph","chromebottom","Mr.","","5554323456","Retirement Planning Co.",null ] );
base.addRow( [ "51","michael#sunrisetravel.com","mike","dolittle","Mr.","",""5552461357","SunRise Travel",null ] );
base.addRow( [ "54","info#lumoxchemical.au","patricia","foxtrot","Mrs,","","5559876543","Lumox Chem Supplies",null ] );
this.query = function() { return " SELECT `u`.* FROM `users` AS `u` WHERE (`deleted`=0) ORDER BY `u`.`lastName` ASC, `u`.`firstName` LIMIT 4"; }
this.url = function() { return "https://www.example.com/DataMgmt.php?fn=fetchCustomerData&sortByFields=lastName,firstName&sortOrder=asc&dynamicdata=13647037920&sessionId=123456789AB\"; }
this.rowCount = function() { return base.rows.length; }
this.colCount = function() { return base.cols.length; }
this.getBase = function() { return base; }
}
*/
In virtually every instance where this code is called, the calling function cannot perform its work until it receives all of the data from the request in the object form that it expects.
So, I've read a bunch of stuff about performing the asynchronous calls, and the necessity to invoke a call-back function that's notified when the data is ready, but I'm a loss as to figuring out a way to return the resultant data back to the original (calling) function that's waiting for it without having to visit every one of those hundreds of instances and make major changes in every one (i.e. change the calling code to expect a call-back function as the result instead of the expected data and act accordingly; times 100's of instances...)
Sooo, any guidance, help or suggestions on how to proceed would be greatly appreciated!

Detect differences between two objects (JSON)

I've got a remote JSON file that contains the list of the last 100 users who logged into a service. This JSON is updated constantly and lists the users from the most recently logged in to the "least recently" logged in.
If the user who appears as number X logs back in, they get removed from their position X and put back at the very top of the JSON at position [0].
I retrieve the JSON every 5 minutes. What I'd like to do is detect the differences between the old object oldUsers and the new newUsers and store them in another object that would only contain the users who are present in newUsers but not in oldUsers. I have no real idea as to how to achieve this.
Here's the JSON structure:
[{
"id":"foo09",
"name":"John",
"age":28
}, {
"id":"bar171",
"name":"Bryan",
"age":36
},
...
]
Is there a rather straightforward way to do it? Thanks!

You need to write your own diff algorithm. Here is one I whipped up in JSBin:
I will need a utility function to merge two arrays (Underscore would help here).
function mergeArrays(val1, val2) {
var results = val1.splice(0);
val2.forEach(function(val) {
if (val1.indexOf(val) < 0) {
results.push(val);
}
});
return results;
}
Diff algorithm
function diff(val1, val2) {
var results = [];
var origKeys = Object.keys(val1);
var newKeys = Object.keys(val2);
mergeArrays(origKeys, newKeys)
.forEach(function(key) {
if (val1[key] === val2[key]) { return; }
var result = {
key: key,
orig: val1[key],
'new': val2[key]
};
if (val1[key] == null) {
result.type = 'add';
} else if (val2[key] == null) {
result.type = 'delete';
} else {
result.type = 'change';
}
results.push(result);
});
return results;
}

Nicer way to get nested object attributes

Often in a response from a remote API call, I receive nested objects:
var response = {
data : {
users : [
{
name : 'Mr. White'
}
]
}
}
I want to check whether the first user's name is 'Mr. White', and would naturally want to write something like.
var existed = response.data.users[0].name === 'Mr. White'
However I cannot be sure if all the objects are present, so to avoid exceptions instead I end up writing:
var existed = response && response.data && response.data.users && response.data.users[0].name === 'Mr. White'
Is there a nicer way to do this? Another ugly option that comes to mind is:
var existed = false;
try {
var existed = response.data.users[0].name === 'Mr. White';
} catch(e) { }
In addition to vanilla javascript, I usually have underscore.js and jquery available too.
Edit:
Oops, noticed I asked a dupe of javascript test for existence of nested object key.
An interesting option based on those answers is:
var existed = (((response || {}).data || {}).users || [{}])[0].name === 'Mr. White';

You could hide this naughty try/catch block inside a function like this one :
function resolve(root, path){
try {
return (new Function(
'root', 'return root.' + path + ';'
))(root);
} catch (e) {}
}
var tree = { level1: [{ key: 'value' }] };
resolve(tree, 'level1[0].key'); // "value"
resolve(tree, 'level1[1].key'); // undefined
More on this : https://stackoverflow.com/a/18381564/1636522

I would use the try catch approach but wrap it in a function to hide the ugliness.

Instead of a try/catch, this should be done via checking whether each level in the object is defined or not.
go for
if(typeof(response)!="undefined"
&& typeof(response.data)!="undefined"
&& typeof(response.data.users)!="undefined"
&& typeof(response.data.users[0])!="undefined"
&& typeof(response.data.users[0].name)!="undefined"
) {
//executes only if response.data.users[0].name is existing
}

Here is a function which I used in one of my projects http://jsfiddle.net/JBBAJ/
var object = {
data: {
users: [
{
firstName: "White"
},
{
firstName: "Black"
}
]
}
}
var read = function(path, obj) {
var path = path.split(".");
var item = path.shift();
if(item.indexOf("]") == item.length-1) {
// array
item = item.split("[");
var arrayName = item.shift();
var arrayIndex = parseInt(item.shift().replace("]", ""));
var arr = obj[arrayName || ""];
if(arr && arr[arrayIndex]) {
return read(path.join("."), arr[arrayIndex]);
} else {
return null;
}
} else {
// object
if(obj[item]) {
if(path.length === 0) {
return obj[item];
} else {
return read(path.join("."), obj[item]);
}
} else {
return null;
}
}
}
console.log(read("data.users[0].firstName", object)); // White
console.log(read("data.users[1].firstName", object)); // Black
console.log(read("data.test.users[0]", object)); // null
The idea is to pass your path as a string along with your object. The idea was to prevent the throwing of an exception and receive just null as result of the path is wrong. The good thing is that the function works with every path and you don't need to write long if statements.