I am running this line:
var good = data["good"] || false;
where data comes from the success method in a jquery ajax request.
But, what I thought that this would do is default good to false if data["good"] is null, but it is not.
Chrome is throwing this:
Uncaught TypeError: Cannot read property 'good' of null
and since it is null, shouldn't good then be set to false?
The problem is not that data["good"] is null, but that data itself is null.
Your code as is would be fine if data always has a value, but may not have property good. But unfortunately the JavaScript engine doesn't check if everything in a statement is undefined or null, i.e. it won't test data, and then test data["good"] and so on.
You need to test if data has at least some sort of value first, that is, it is "truthy".
Fix 1
You can lay it out clearly like so:
var good = false;
if(data && data["good"]) {
good = data["good"];
}
Fix 2
Or a neat shortcut is to use the fact that && and || will return the first "truthy" value found - it does not have to be a boolean:
var good = (data && data["good"]) || false;
The jquery tutorial on Operators has a good explanation of what is returned from the && and || operators.
// has a value - sets to "foo"
var data1 = { good: 'foo' };
var good1 = (data1 && data1["good"]) || false;
document.write("<div>" + good1 + "</div>");
// data is null - sets to false
var data2 = null;
var good2 = (data2 && data2["good"]) || false;
document.write("<div>" + good2 + "</div>");
// data["good"] doesn't exist - sets to false
var data3 = { bad: 'hello' };
var good3 = (data3 && data3["good"]) || false;
document.write("<div>" + good3 + "</div>");
Falsy Gotchas!
The other thing to be careful of is that some values you would want to store in your variable may evaluate to false, so you might incorrectly end up with good = false. This depends on what you expect to be inside data["good"].
This will occur for the following, again from the jquery site:
false - boolean false value
"" - Empty strings
NaN - "not-a-number"
null - null values
undefined - undefined values (i.e. if data doesn't have property "good")
0 - the number zero.
If you think this could be the case, you may need to be more specific in your checks:
var data = { good: 0 };
// 0 is falsy, so incorrectly sets to false
var good = (data && data["good"]) || false;
document.write("<div>" + good + "</div>");
// check the actual type and value - correctly set to 0
var good2 = (data && (typeof data["good"] != "undefined") && data["good"] != null)
? data["good"] : false;
document.write("<div>" + good2 + "</div>");
In your case, I can't imagine one-liner, which will check if data is not null and if so, put data[good] into variable.
You must first of all, get rid of Exception.
I would rather do:
var good = false;
if(data){
good = data["good"] || false;
}
Related
I'm populating a table with data - using fixed-data-table, which is a React.js component. However, that isn't so important at this stage.
The table has a search box where the issue stems from.
First, here's the interesting part of the code.
for (var index = 0; index < size; index++) {
if (!filterBy || filterBy == undefined) {
filteredIndexes.push(index);
}
else {
var backendInfo = this._dataList[index];
var userListMap = hostInfo.userList;
var userListArr = Object.values(userListMap);
function checkUsers(){
for (var key in userListArr) {
if (userListArr.hasOwnProperty(key) && userListArr[key].text.toLowerCase().indexOf(filterBy) !== -1) {
return true;
}
}
return false;
}
if (backendInfo.firstName.indexOf(filterBy) !== -1 || backendInfo.lastName.toLowerCase().indexOf(filterBy) !== -1 || backendInfo.countryOrigin.toLowerCase().indexOf(filterBy) !== -1
|| backendInfo.userListMap.indexOf(filterBy) !== -1) {
filteredIndexes.push(index);
}
}
}
This is rendered and the last part is throwing errors if you input something in the table, and a column returns null from the user input.
The thing is, I can make the code work if I change the last part to ..
try {
if (backendInfo.firstName.indexOf(filterBy) !== -1 || backendInfo.lastName.toLowerCase().indexOf(filterBy) !== -1 || backendInfo.countryOrigin.toLowerCase().indexOf(filterBy) !== -1
|| backendInfo.userListMap.indexOf(filterBy) !== -1) {
filteredIndexes.push(index);
}
}
catch(err) {
console.log('Exception')
}
With the try/catch, it works 100% as intended and handles the indexOf returning null... But this can't be the way to properly handle it - I'm assuming this sort of exception handling is, well, supposed to be for rare exceptions, and shouldn't really be used on the front-end as much as the backend.
How do I handle indexOf returning null in the above Javascript code? It might return null in any of the sources columns that are being populated.
If a key cannot be found, JS will throw an error. Try-catch is a good way to fix these errors, but there is an alternative:
You could check if keys exist in an object prior to pushing a value into it.
var data = { };
var key = "test";
// your method works great
try {
var value = data.firstname.indexOf(key);
} catch (err) {}
// another method, I'd prefer the try/catch
var value = data.firstname ? data.firstname.indexOf(key) : undefined;
// test if the object is the type of object you are looking for
// this is in my opinion the best option.
if(data.firstname instanceof Array){
var value = data.firstname.indexOf(key);
}
// you can use the last option in your code like this:
var firstnameHasKey = data.firstname instanceof Array && ~data.firstname.indexOf(key);
var lastnameHasKey = data.lastname instanceof Array && ~data.lastname.indexOf(key);
if(firstnameHasKey || lastnameHasKey){
// logics
}
If you test the instanceof && indexOf, there will never be an error. If firstname is undefined, the indexOf will never be checked.
Ofcourse you can use this for other types:
var myDate = new Date();
myDate instanceof Date; // returns true
myDate instanceof Object; // returns true
myDate instanceof String; // returns false
MDN documentation
I get return value as null and assign that value it shows as null in the UI. But I want to check some condition and if it is null, it should not show up anything..
I tried the below code and it doesn't work
var companyString;
if(utils.htmlEncode(item.companyname) == null)
{
companyString = '';
}
else{
companyString = utils.htmlEncode(item.companyname);
}
Compare item.companyname to null (but probably really any false-y value) - and not the encoded form.
This is because the encoding will turn null to "null" (or perhaps "", which are strings) and "null" == null (or any_string == null) is false.
Using the ternary operator it can be written as so:
var companyString = item.companyname
? utils.htmlEncode(item.companyname)
: "";
Or with coalescing:
var companyString = utils.htmlEncode(item.companyname ?? "");
Or in a long-hand form:
var companyString;
if(item.companyname) // if any truth-y value then encode
{
companyString = utils.htmlEncode(item.companyname);
}
else{ // else, default to an empty string
companyString = '';
}
var companyString;
if(item.companyname !=undefined && item.companyname != null ){
companyString = utils.htmlEncode(item.companyname);
}
else{
companyString = '';
}
Better to check not undefined along with not null in case of javascript. And you can also put alert or console.logto check what value you are getting to check why your if block not working. Also, utls.htmlEncode will convert your null to String having null literal , so compare without encoding.
var companyString="";
if(utils.htmlEncode(item.companyname) != null)
{
companyString = utils.htmlEncode(item.companyname);
}
here's my function for checking zipcode. When a null values comes in, i keep getting "Object Required" Does anyone know where im going wrong?
aspx tags -
asp:CustomValidator
ID="cv_zipcode"
runat="server"
ControlToValidate="tb_zipcode"
ClientValidationFunction="ValidateZipcode"
ValidateEmptyText="true"
Display="Dynamic"
ValidationGroup="vgroup">
</asp:CustomValidator>
function ValidateZipcode(sender, args) {
var regZipcode = '\d{5}'
var zipcode = document.getElementById(sender.id.replace(/cv_/, "tb_"));
if ((zipcode.value == "ZipCode") || (zipcode.value.length == null) || (zipcode.value.length == "")) {
zipcode.style.backgroundColor = "#f6e086";
args.IsValid = false; return;
} else {
args.IsValid = true;
zipcode.style.backgroundColor = "white";
}
}
I'm not sure exactly which value is null, but in general, if you have a variable x which may or may not be null, and you want to do something with x, you can do the following:
x != null && do_something_with(x)
If x == null, then this returns false and doesn't try to execute do_something_with(). Otherwise, this expression returns the value of do_something_with(x).
If you just do_something_with(x), and x is null, and do_something_with() is not expecting a null, you can get errors.
EDIT:
try:
if ((zipcode == null) || (zipcode.value == null) || [everything else])
zipcode.value.length returns an integer
I think you should have
if ((zipcode.value == "ZipCode") || (zipcode.value.length == 0))
I would be a little suspect of this line:
if ((zipcode.value == "ZipCode") || (zipcode.value.length == null) || (zipcode.value.length == "")) {
Try this instead:
if ((zipCode.value == null) || (zipcode.value== "") || (zipcode.value.length == 0)) {
That error message usually indicates that you've tried to get or set a property or call a method of something that isn't an object, which tends to happen when a variable that you thought referred to an object is actuall null or undefined. That is, if someVariable is null or undefined then you can't say someVariable.someProperty.
If .getElementById() doesn't find a matching element it returns null, so in this line:
var zipcode = document.getElementById(sender.id.replace(/cv_/, "tb_"));
zipcode is potentially set to null, and if it is then all attempts to access properties of zipcode like zipcode.value and zipcode.style will fail.
If the parameter args comes in as null or undefined then attempting to set args.IsValid will fail, and similarly if the parameter sender is null or undefined then sender.id will fail.
So, if you have a variable that might be null you should test that before trying to do anything else with it.
AddPatient = {};
AddPatient.Firstname = FirstNameValue || PatientModel.errorMsg('FirstName',FirstNameValue);
AddPatient.LastName = LastNameValue || PatientModel.errorMsg('LastName',LastNameValue);
AddPatient is an Object and i am checking it whether its blank or not before sending the request.
PatientModel.js
errorMsg: function(title,FirstNameValue,LastNameValue) {
if(FirstNameValue === undefined || FirstNameValue === ' ' && LastNameValue === undefined || LastNameValue = ' ') {
alert('FirstName and LastName are missing');
return false;
} else {
alert(+title 'is missing');
return false;
}
}
I have a form, where i have FirstName and LastName field and i have to check it should not be blank. I want a single function in javascript which can work.
Is this the right way to do it?
I can see a couple of problems in your code.
Mismatch between errorMsg()'s expected arguments and how it is called
Syntax error in second alert()
Bad expression inside if statement
Mismatch between errorMsg()'s expected arguments and how it is called
Your errorMsg() function expects three arguments, but you only pass it two at a time:
errorMsg: function(title,FirstNameValue,LastNameValue) {
....
}
... and then ....
.errorMsg('FirstName',FirstNameValue);
.errorMsg('FirstName',LastNameValue);
If you really want to use both values inside errorMsg(), you need to pass them both every time, in the same order the function expects them:
PatientModel.errorMsg('FirstName',FirstNameValue,LastNameValue);
PatientModel.errorMsg('LastName',FirstNameValue,LastNameValue);
// This is weird code, but it'll work
Syntax error in second alert()
This is simple enough to fix, and could have been just a typo.
alert(+title 'is missing');
^ ^_There's something missing here.
|_This will only try to convert title to a number
What you want is this:
alert(title + 'is missing');
Bad expression inside if statement
if(FirstNameValue === undefined || FirstNameValue === ' ' && LastNameValue === undefined || LastNameValue = ' ') {
This won't work as you expect, because && has greater precedence than ||, meaning the expression will be evaluated as such:
if (
FirstNameValue === undefined
|| (FirstNameValue === ' ' && LastNameValue === undefined)
|| LastNameValue = ' '
) {
You would need parenthesis to fix the precedence:
if( (FirstNameValue === undefined || FirstNameValue === ' ') && (LastNameValue === undefined || LastNameValue = ' ') ) {
This is irrelevant, actually, because the expression can be simplified like this:
// If these values are taken from a form input, they are guaranteed to be strings.
if(FirstNameValue.length === 0 && LastNameValue.length === 0) {
Or even better, like this:
// Uses regular expressions to checks if string is not whitespace only
var WHITESPACE = /^\s*$/;
if( WHITESPACE.test(FirstNameValue) && WHITESPACE.test(FirstNameValue)){
How I would fix your code
This would be an incomplete answer if I didn't provide a correct version of your code, so here it goes. Notice that I separate filling-in of information and its validation in two steps.
PatientModel.js :
validate: function(patient){
var WHITESPACE = /^\s*$/;
var errors = [];
if( WHITESPACE.test(patient.FirstName) ){
// No first name
if( WHITESPACE.test(patient.LastName) ){
// No last name either
errors.push('FirstName and LastName are missing');
}
else {
// Only first name missing
errors.push('FirstName is missing');
}
}
else if( WHITESPACE.test( patient.LastName) ){
// Only last name missing
errors.push('LastName is missing');
}
// Returns array of errors
return errors;
}
Your other code:
AddPatient = {};
AddPatient.Firstname = FirstNameValue;
AddPatient.LastName = LastNameValue;
errors = PatientModel.validate(AddPatient);
if( errors.length != 0 ){
alert('You have the following errors:\n' + errors.join('\n'));
}
Edit: a different, perhaps better, approach. The only difference is we now write validate() as a method of a Patient object:
>>> PatientModel.js:
var WHITESPACE = /^\s*$/;
// Creates a new empty Patient
function Patient(){
this.FirstName = '';
this.LastName = '';
}
// Adds a validate() method to all Patient instances
Patient.prototype.validate: function(){
var errors = [];
if( WHITESPACE.test(this.FirstName) ){
// No first name
if( WHITESPACE.test(this.LastName) ){
// No last name either
errors.push('FirstName and LastName are missing');
}
else {
// Only first name missing
errors.push('FirstName is missing');
}
}
else if( WHITESPACE.test( thisLastName) ){
// Only last name missing
errors.push('LastName is missing');
}
// Returns array of errors
return errors;
}
>>> Your other code :
patient = new Patient();
patient.FirstName = FirstNameValue;
patient.LastName = LastNameValue;
errors = patient.validate();
if( errors.length != 0 ){
alert('You have the following errors:\n' + errors.join('\n'));
}
I would recommend using the Jquery validate plugin for this functionality. It will let you do a hole range of clientside validation. Including required validation.
If you just want pure javascript then your method is fine. I'd make it a more generic validate method which would check each validation rule you have and if it fails add the message to an array. After all your checks are finished if the count of the array is grater then zero then output complete list of errors.
Can I use 'in' to check existence of non top level names in a JSON data structure in a single comparison?
I have n tier JSON data structures,
I can do: if("mbled" in jsonData), works fine
For a lower tier name:
I can do this but (works but gets clunky as I go deeper): if("pnpenvsense1" in jsonData && "light" in jsonData.pnpenvsense1)
I'd prefer something like (doesn't work, always returns false): if("pnpenvsense1.light" in jsonData)
something like:
function objExists(path, struct){
path = path.split('.');
for(var i=0, l=path.length; i<l; i++){
if(!struct.hasOwnProperty(path[i])){ return false; }
struct = struct[path[i]];
}
return true;
}
objExists('pnpenvsense1.light', jsonData);
try
// will check if it is defined and not false
if(pnpenvsense1.light !== undefined && pnpenvsense1.light != false )
{ // my code }
http://jsfiddle.net/
arr = new Array();
arr['myKey'] = 12;
arr['myOtherKey'] = { "first" : "yes" , "second" : false };
if(arr.myKey !== undefined && arr.myKey != false)
alert("1 -> " + arr.myKey);
if(arr.myOtherKey.first !== undefined && arr.myOtherKey.first != false)
alert("2 -> " + arr.myOtherKey.first);