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When trying to push items to an array in javascripts it gives an error, the following pseudo code illustrate what is happening:
var data = new Array();
for(...) {
data[key].push(item[i]);
}
It is showing the following error:
Cannot read property 'push' of undefined
Thanks
If you need a 2d array, you have to initialize each element of the outer array to be an array.
// Have to check every array item, if it's not an array already, make it so
for(...) {
if (!data[key]) {
data[key] = [];
}
data[key].push(item[i]);
}
You could always do the following if you know the number of inner arrays you need:
var data = [[],[],[],[],[],[]];
In your example, since they variable name is key, I'm assuming you actually want an object of arrays. If you know the keys ahead of time, you can use the following literal.
var data = {
myKey1: [],
myKey2: []
}
Related
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I need to get the result of this object, I've tried json.count(id_reported) and json['count(id_reported)'] but none worked.
const json = {
'count(id_reported)': 21
};
//console.log(json.count(id_reported));
console.log(json['count(id_reported)']);
In Javascript, Typescript and so in Express in the end, its easy to handle such things.
var myObject = {
'count': 21
}
myObject = JSON.parse(myObject);
console.log(myObject.count);
The JSON.parse is only needed, if you object is a string. Is it a Javascript object you do not need to parse.
The count(id_reported) part I don't understand. If your object looks like this in the end:
{
count(1): 1,
count(2): 2,
}
and you don't know the structure at all you can use a for loop:
for (let data in myObject) {
console.log(data); // data will be the key; so count(1) as example
}
See the in keyword in the for loop. This will give you the key. The on keyword otherwise gives the object in an array as example.
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var teacherArray=[];
I have created an array variable.
I am creating an array with the key and value. and pushing these data to the teacherArray.
random={
teacherId:TeacherId,
day:day,
periodCount:period,
class:Studentclass,
section:Studentsection,
startTime:schoolStartTime,
endTime:schoolEndTime
};
teacherArray.push(random);
console.log(teacherArray);
In the console I am able to see the created array. But when the submit button clicked i am calling the array like
teacherLength=teacherArray.length;
for (let k=0;k<=teacherLength;k++)
{
var teachId=teacherArray[k].teacherId;
console.log(teachId);
}
In the console displays the teacherId, but next line shows the error as
TypeError: Cannot read property 'teacherId' of undefined
Arrays are zero index based. So when you write k<=teacherLength you are requesting more than what array have. That should be changed to
k<teacherLength
Arrays are 0 indexed. You are having,
for (let k=0;k<=teacherLength;k++)
Make it,
for (let k=0;k<teacherLength;k++)
Your code is reading an extra item, you need to replace
for (let k=0;k<=teacherLength;k++)
with
for (let k=0;k<teacherLength;k++) //notice < instead of <=
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For some reason I need to push an Array inside other array.
For example,
var a = ["Test1", 1];
var b = ["Test2", 2];
var c = [];
c.push(a);
c.push(b);
alert(c);
For this code I need the following output,
["Test1", 1],["Test2", 2]
But what I am getting is
Test1,1,Test2,2
Any help will be highly appreciable.
You've already done it correctly: c.push(a) and c.push(b) work, but you don't want to use alert() for debugging.
Though it might be more convenient since you don't have to open up a console, it's going to give you output that is inconsistent with the actual structure of the data because using alert(x) converts whatever x is to a string.
Always use console.log(). Had you done that in this case, you would have seen something like this in the console:
Demo
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I have a variable which looks like this when I log it:
console.log(msg)
["The Email must be at least 10 characters long."]
I thought this meant that the text is inside an array as the 1st and only element. However
when I try to get the first element it gives me:
console.log(msg.[0]))
SyntaxError: Unexpected token [
How can I extract the text from the msg variable?
To get the contents of an array:
for (var i = 0; i < yourArray.length; i++) {
console.log(yourArray[i]);
}
To get the contents of an object:
for (var obj in myObject) {
console.log(obj);
}
You're syntax is wrong, instead you need:
console.log(msg[0]))
[] accessors are used for array access, or to access an object property via a string myObj["value"]
. accessors are used for fields when you know the name so you could use myObj.value
simply remove the . when accessing individual array elements.
therefore it becomes :
console.log(msg[0]);
Take the dot in msg.[0] out.
console.log(msg[0])
should retrieve your text correctly.
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I am tying to add a property to a JS object inside a function. I can do it outside but not inside. Please explain. Sorry. I am missing something very basic here.
var newobj = {'prop1' : 12, 'prop2' : 25};
myfunc(newobj);
function myfunc(someobj) {
someobj.prop3 = 45;
}
This gives a syntax error.
Chances are something else is interfering because it works for me.
If you dump newobj before the function call you get:
{"prop1":12,"prop2":25}
And after the function call:
{"prop1":12,"prop2":25,"prop3":45}
As you can see, the new property has been added.
I would suggest either looking at what you have more closesly (make sure you're not copying the value and then passing it) or add some console.log call in your code as it goes through. You can also, in most of the browsers, use the debugger to step through the code to see where it may be fouled.