Using Variable for Property Name of Object - Javascript [duplicate] - javascript

This question already has an answer here:
How to use the value of a variable in creating an object in JavaScript [duplicate]
(1 answer)
Closed 9 years ago.
saw a few answers related to this, but none answer this version of the subject in question.
Consider the following: (linkto: jsfiddle)
$(function(){
arrKeys = [];
objArr = [];
nameArr = ['name1','name2','name3','name4'];
descArr = ['desc1','desc2','desc3','desc4'];
allValues = {name: nameArr, desc: descArr};
arrKeys[0] = 'name';
arrKeys[1] = 'desc';
first = arrKeys.shift(); // returns 'name'
$(allValues[first]).each(function (key,value) {
console.log(first); //returns 'name'
objArr[key] = {first:value}; //the problem
});
console.log(objArr);
});
With console.log(objArr) producing the following array of objects like so:
[Object, Object, Object, Object]
0: Object
first: "name1"
1: Object
first: "name2"
2: Object
first: "name3"
3: Object
first: "name4"
length: 4
The issue is that I'd like the property "first" to be the value of the var first (which is "name".. So instead, the result would be:
[Object, Object, Object, Object] 0: Object
name: "name1" 1: Object
name: "name2" 2: Object
name: "name3" 3: Object
name: "name4" length: 4
(linkto: jsfiddle)

To set variables as key names you have to use bracket notation;
console.log(first); // returns 'name'
var obj = {};
obj[first] = value;
objArr[key] = obj; // no longer a problem
Sorry it's more verbose :(
Edit;
In ES6 you can now use computed-property-names;
const key = 'name';
const value = 'james';
const obj = {
[key]: value
};

var x = {}
x[first] = value
objArr[key] = x
Javascript object literal syntax treats unquoted keys as if they were quoted strings instead of variable names. You have to use bracket syntax to set properties with names computed at runtime.
(Why are you wrapping your code in a jQuery call? And you really should be using var declarations.)

Related

javascript map(val , index) , which condition val is variable and string [duplicate]

This question already has answers here:
Accessing an object property with a dynamically-computed name
(19 answers)
Closed 4 months ago.
I'm pulling items out of the DOM with jQuery and want to set a property on an object using the id of the DOM element.
Example
const obj = {}
jQuery(itemsFromDom).each(function() {
const element = jQuery(this)
const name = element.attr('id')
const value = element.attr('value')
// Here is the problem
obj.name = value
})
If itemsFromDom includes an element with an id of "myId", I want obj to have a property named "myId". The above gives me name.
How do I name a property of an object using a variable using JavaScript?
You can use this equivalent syntax:
obj[name] = value
Example:
let obj = {};
obj["the_key"] = "the_value";
or with ES6 features:
let key = "the_key";
let obj = {
[key]: "the_value",
};
in both examples, console.log(obj) will return: { the_key: 'the_value' }
With ECMAScript 2015 you can do it directly in object declaration using bracket notation:
var obj = {
[key]: value
}
Where key can be any sort of expression (e.g. a variable) returning a value:
var obj = {
['hello']: 'World',
[x + 2]: 42,
[someObject.getId()]: someVar
}
You can even make List of objects like this
var feeTypeList = [];
$('#feeTypeTable > tbody > tr').each(function (i, el) {
var feeType = {};
var $ID = $(this).find("input[id^=txtFeeType]").attr('id');
feeType["feeTypeID"] = $('#ddlTerm').val();
feeType["feeTypeName"] = $('#ddlProgram').val();
feeType["feeTypeDescription"] = $('#ddlBatch').val();
feeTypeList.push(feeType);
});
There are two different notations to access object properties
Dot notation: myObj.prop1
Bracket notation: myObj["prop1"]
Dot notation is fast and easy but you must use the actual property name explicitly. No substitution, variables, etc.
Bracket notation is open ended. It uses a string but you can produce the string using any legal js code. You may specify the string as literal (though in this case dot notation would read easier) or use a variable or calculate in some way.
So, these all set the myObj property named prop1 to the value Hello:
// quick easy-on-the-eye dot notation
myObj.prop1 = "Hello";
// brackets+literal
myObj["prop1"] = "Hello";
// using a variable
var x = "prop1";
myObj[x] = "Hello";
// calculate the accessor string in some weird way
var numList = [0,1,2];
myObj[ "prop" + numList[1] ] = "Hello";
Pitfalls:
myObj.[xxxx] = "Hello"; // wrong: mixed notations, syntax fail
myObj[prop1] = "Hello"; // wrong: this expects a variable called prop1
tl;dnr: If you want to compute or reference the key you must use bracket notation. If you are using the key explicitly, then use dot notation for simple clear code.
Note: there are some other good and correct answers but I personally found them a bit brief coming from a low familiarity with JS on-the-fly quirkiness. This might be useful to some people.
With lodash, you can create new object like this _.set:
obj = _.set({}, key, val);
Or you can set to existing object like this:
var existingObj = { a: 1 };
_.set(existingObj, 'a', 5); // existingObj will be: { a: 5 }
You should take care if you want to use dot (".") in your path, because lodash can set hierarchy, for example:
_.set({}, "a.b.c", "d"); // { "a": { "b": { "c": "d" } } }
First we need to define key as variable and then we need to assign as key as object., for example
var data = {key:'dynamic_key',value:'dynamic_value'}
var key = data.key;
var obj = { [key]: data.value}
console.log(obj)
Related to the subject, not specifically for jquery though. I used this in ec6 react projects, maybe helps someone:
this.setState({ [`${name}`]: value}, () => {
console.log("State updated: ", JSON.stringify(this.state[name]));
});
PS: Please mind the quote character.
With the advent of ES2015 Object.assign and computed property names the OP's code boils down to:
var obj = Object.assign.apply({}, $(itemsFromDom).map((i, el) => ({[el.id]: el.value})));
ajavascript have two type of annotation for fetching javascript Object properties:
Obj = {};
1) (.) annotation eg. Obj.id
this will only work if the object already have a property with name 'id'
2) ([]) annotation eg . Obj[id] here if the object does not have any property with name 'id',it will create a new property with name 'id'.
so for below example:
A new property will be created always when you write Obj[name].
And if the property already exist with the same name it will override it.
const obj = {}
jQuery(itemsFromDom).each(function() {
const element = jQuery(this)
const name = element.attr('id')
const value = element.attr('value')
// This will work
obj[name]= value;
})
If you want to add fields to an object dynamically, simplest way to do it is as follows:
let params = [
{ key: "k1", value: 1 },
{ key: "k2", value: 2 },
{ key: "k3", value: 3 },
];
let data = {};
for (let i = 0; i < params.length; i++) {
data[params[i].key] = params[i].value;
}
console.log(data); // -> { k1: 1, k2: 2, k3: 3 }
The 3 ways to access the object value
We can output the object value by passing in the appropriate key. Because I used emoji as the key in my example, it's a bit tricky. So let's look at a easier example.
let me = {
name: 'samantha',
};
// 1. Dot notation
me.name; // samantha
// 2. Bracket notation (string key)
me['name']; // samantha
// 3. Bracket notation (variable key)
let key = 'name';
me[key]; // samantha
know more
If you have object, you can make array of keys, than map through, and create new object from previous object keys, and values.
Object.keys(myObject)
.map(el =>{
const obj = {};
obj[el]=myObject[el].code;
console.log(obj);
});
objectname.newProperty = value;
const data = [{
name: 'BMW',
value: '25641'
}, {
name: 'Apple',
value: '45876'
},
{
name: 'Benz',
value: '65784'
},
{
name: 'Toyota',
value: '254'
}
]
const obj = {
carsList: [{
name: 'Ford',
value: '47563'
}, {
name: 'Toyota',
value: '254'
}],
pastriesList: [],
fruitsList: [{
name: 'Apple',
value: '45876'
}, {
name: 'Pineapple',
value: '84523'
}]
}
let keys = Object.keys(obj);
result = {};
for(key of keys){
let a = [...data,...obj[key]];
result[key] = a;
}

JavaScript: Fetch Headers: Object literal does not add custom header, new Header() obj does [duplicate]

This question already has answers here:
Accessing an object property with a dynamically-computed name
(19 answers)
Closed 4 months ago.
I'm pulling items out of the DOM with jQuery and want to set a property on an object using the id of the DOM element.
Example
const obj = {}
jQuery(itemsFromDom).each(function() {
const element = jQuery(this)
const name = element.attr('id')
const value = element.attr('value')
// Here is the problem
obj.name = value
})
If itemsFromDom includes an element with an id of "myId", I want obj to have a property named "myId". The above gives me name.
How do I name a property of an object using a variable using JavaScript?
You can use this equivalent syntax:
obj[name] = value
Example:
let obj = {};
obj["the_key"] = "the_value";
or with ES6 features:
let key = "the_key";
let obj = {
[key]: "the_value",
};
in both examples, console.log(obj) will return: { the_key: 'the_value' }
With ECMAScript 2015 you can do it directly in object declaration using bracket notation:
var obj = {
[key]: value
}
Where key can be any sort of expression (e.g. a variable) returning a value:
var obj = {
['hello']: 'World',
[x + 2]: 42,
[someObject.getId()]: someVar
}
You can even make List of objects like this
var feeTypeList = [];
$('#feeTypeTable > tbody > tr').each(function (i, el) {
var feeType = {};
var $ID = $(this).find("input[id^=txtFeeType]").attr('id');
feeType["feeTypeID"] = $('#ddlTerm').val();
feeType["feeTypeName"] = $('#ddlProgram').val();
feeType["feeTypeDescription"] = $('#ddlBatch').val();
feeTypeList.push(feeType);
});
There are two different notations to access object properties
Dot notation: myObj.prop1
Bracket notation: myObj["prop1"]
Dot notation is fast and easy but you must use the actual property name explicitly. No substitution, variables, etc.
Bracket notation is open ended. It uses a string but you can produce the string using any legal js code. You may specify the string as literal (though in this case dot notation would read easier) or use a variable or calculate in some way.
So, these all set the myObj property named prop1 to the value Hello:
// quick easy-on-the-eye dot notation
myObj.prop1 = "Hello";
// brackets+literal
myObj["prop1"] = "Hello";
// using a variable
var x = "prop1";
myObj[x] = "Hello";
// calculate the accessor string in some weird way
var numList = [0,1,2];
myObj[ "prop" + numList[1] ] = "Hello";
Pitfalls:
myObj.[xxxx] = "Hello"; // wrong: mixed notations, syntax fail
myObj[prop1] = "Hello"; // wrong: this expects a variable called prop1
tl;dnr: If you want to compute or reference the key you must use bracket notation. If you are using the key explicitly, then use dot notation for simple clear code.
Note: there are some other good and correct answers but I personally found them a bit brief coming from a low familiarity with JS on-the-fly quirkiness. This might be useful to some people.
With lodash, you can create new object like this _.set:
obj = _.set({}, key, val);
Or you can set to existing object like this:
var existingObj = { a: 1 };
_.set(existingObj, 'a', 5); // existingObj will be: { a: 5 }
You should take care if you want to use dot (".") in your path, because lodash can set hierarchy, for example:
_.set({}, "a.b.c", "d"); // { "a": { "b": { "c": "d" } } }
First we need to define key as variable and then we need to assign as key as object., for example
var data = {key:'dynamic_key',value:'dynamic_value'}
var key = data.key;
var obj = { [key]: data.value}
console.log(obj)
Related to the subject, not specifically for jquery though. I used this in ec6 react projects, maybe helps someone:
this.setState({ [`${name}`]: value}, () => {
console.log("State updated: ", JSON.stringify(this.state[name]));
});
PS: Please mind the quote character.
With the advent of ES2015 Object.assign and computed property names the OP's code boils down to:
var obj = Object.assign.apply({}, $(itemsFromDom).map((i, el) => ({[el.id]: el.value})));
ajavascript have two type of annotation for fetching javascript Object properties:
Obj = {};
1) (.) annotation eg. Obj.id
this will only work if the object already have a property with name 'id'
2) ([]) annotation eg . Obj[id] here if the object does not have any property with name 'id',it will create a new property with name 'id'.
so for below example:
A new property will be created always when you write Obj[name].
And if the property already exist with the same name it will override it.
const obj = {}
jQuery(itemsFromDom).each(function() {
const element = jQuery(this)
const name = element.attr('id')
const value = element.attr('value')
// This will work
obj[name]= value;
})
If you want to add fields to an object dynamically, simplest way to do it is as follows:
let params = [
{ key: "k1", value: 1 },
{ key: "k2", value: 2 },
{ key: "k3", value: 3 },
];
let data = {};
for (let i = 0; i < params.length; i++) {
data[params[i].key] = params[i].value;
}
console.log(data); // -> { k1: 1, k2: 2, k3: 3 }
The 3 ways to access the object value
We can output the object value by passing in the appropriate key. Because I used emoji as the key in my example, it's a bit tricky. So let's look at a easier example.
let me = {
name: 'samantha',
};
// 1. Dot notation
me.name; // samantha
// 2. Bracket notation (string key)
me['name']; // samantha
// 3. Bracket notation (variable key)
let key = 'name';
me[key]; // samantha
know more
If you have object, you can make array of keys, than map through, and create new object from previous object keys, and values.
Object.keys(myObject)
.map(el =>{
const obj = {};
obj[el]=myObject[el].code;
console.log(obj);
});
objectname.newProperty = value;
const data = [{
name: 'BMW',
value: '25641'
}, {
name: 'Apple',
value: '45876'
},
{
name: 'Benz',
value: '65784'
},
{
name: 'Toyota',
value: '254'
}
]
const obj = {
carsList: [{
name: 'Ford',
value: '47563'
}, {
name: 'Toyota',
value: '254'
}],
pastriesList: [],
fruitsList: [{
name: 'Apple',
value: '45876'
}, {
name: 'Pineapple',
value: '84523'
}]
}
let keys = Object.keys(obj);
result = {};
for(key of keys){
let a = [...data,...obj[key]];
result[key] = a;
}

How to access props inside a filter with an argument in React [duplicate]

This question already has answers here:
Add a property to a JavaScript object using a variable as the name? [duplicate]
(14 answers)
Closed 7 years ago.
I want to add a new property to 'myObj', name it 'string1' and give it a value of 'string2', but when I do it it returns 'undefined:
var myObj = new Object;
var a = 'string1';
var b = 'string2';
myObj.a = b;
alert(myObj.string1); //Returns 'undefined'
alert(myObj.a); //Returns 'string2'
In other words: How do I create an object property and give it the name stored in the variable, but not the name of the variable itself?
There's the dot notation and the bracket notation
myObj[a] = b;
ES6 introduces computed property names, which allow you to do
var myObj = {[a]: b};
Dot notation and the properties are equivalent. So you would accomplish like so:
// const myObj = new Object();
const myObj = {};
const a = 'string1';
myObj[a] = 'whatever';
alert(myObj.string1);
(alerts "whatever")
Ecu, if you do myObj.a, then it looks for the property named a of myObj.
If you do myObj[a] =b then it looks for the a.valueOf() property of myObj.
Oneliner:
obj = (function(attr, val){ var a = {}; a[attr]=val; return a; })('hash', 5);
Or:
attr = 'hash';
val = 5;
var obj = (obj={}, obj[attr]=val, obj);
Anything shorter?
You could just use this:
function createObject(propName, propValue){
this[propName] = propValue;
}
var myObj1 = new createObject('string1','string2');
Anything you pass as the first parameter will be the property name, and the second parameter is the property value.
You cannot use a variable to access a property via dot notation, instead use the array notation.
var obj= {
'name' : 'jroi'
};
var a = 'name';
alert(obj.a); //will not work
alert(obj[a]); //should work and alert jroi'
As $scope is an object, you can try with JavaScript by:
$scope['something'] = 'hey'
It is equal to:
$scope.something = 'hey'
I created a fiddle to test.
The following demonstrates an alternative approach for returning a key pair object using the form of (a, b). The first example uses the string 'key' as the property name, and 'val' as the value.
Example #1:
(function(o,a,b){return o[a]=b,o})({},'key','val');
Example: #2:
var obj = { foo: 'bar' };
(function(o,a,b){return o[a]=b,o})(obj,'key','val');
As shown in the second example, this can modify existing objects, too (if property is already defined in the object, value will be overwritten).
Result #1: { key: 'val' }
Result #2: { foo: 'bar', key: 'val' }

JS using a variable name as a key in an array [duplicate]

This question already has answers here:
Add a property to a JavaScript object using a variable as the name? [duplicate]
(14 answers)
Closed 7 years ago.
I want to add a new property to 'myObj', name it 'string1' and give it a value of 'string2', but when I do it it returns 'undefined:
var myObj = new Object;
var a = 'string1';
var b = 'string2';
myObj.a = b;
alert(myObj.string1); //Returns 'undefined'
alert(myObj.a); //Returns 'string2'
In other words: How do I create an object property and give it the name stored in the variable, but not the name of the variable itself?
There's the dot notation and the bracket notation
myObj[a] = b;
ES6 introduces computed property names, which allow you to do
var myObj = {[a]: b};
Dot notation and the properties are equivalent. So you would accomplish like so:
// const myObj = new Object();
const myObj = {};
const a = 'string1';
myObj[a] = 'whatever';
alert(myObj.string1);
(alerts "whatever")
Ecu, if you do myObj.a, then it looks for the property named a of myObj.
If you do myObj[a] =b then it looks for the a.valueOf() property of myObj.
Oneliner:
obj = (function(attr, val){ var a = {}; a[attr]=val; return a; })('hash', 5);
Or:
attr = 'hash';
val = 5;
var obj = (obj={}, obj[attr]=val, obj);
Anything shorter?
You could just use this:
function createObject(propName, propValue){
this[propName] = propValue;
}
var myObj1 = new createObject('string1','string2');
Anything you pass as the first parameter will be the property name, and the second parameter is the property value.
You cannot use a variable to access a property via dot notation, instead use the array notation.
var obj= {
'name' : 'jroi'
};
var a = 'name';
alert(obj.a); //will not work
alert(obj[a]); //should work and alert jroi'
As $scope is an object, you can try with JavaScript by:
$scope['something'] = 'hey'
It is equal to:
$scope.something = 'hey'
I created a fiddle to test.
The following demonstrates an alternative approach for returning a key pair object using the form of (a, b). The first example uses the string 'key' as the property name, and 'val' as the value.
Example #1:
(function(o,a,b){return o[a]=b,o})({},'key','val');
Example: #2:
var obj = { foo: 'bar' };
(function(o,a,b){return o[a]=b,o})(obj,'key','val');
As shown in the second example, this can modify existing objects, too (if property is already defined in the object, value will be overwritten).
Result #1: { key: 'val' }
Result #2: { foo: 'bar', key: 'val' }

Add a property to a JavaScript object using a variable as the name? [duplicate]

This question already has answers here:
Accessing an object property with a dynamically-computed name
(19 answers)
Closed 4 months ago.
I'm pulling items out of the DOM with jQuery and want to set a property on an object using the id of the DOM element.
Example
const obj = {}
jQuery(itemsFromDom).each(function() {
const element = jQuery(this)
const name = element.attr('id')
const value = element.attr('value')
// Here is the problem
obj.name = value
})
If itemsFromDom includes an element with an id of "myId", I want obj to have a property named "myId". The above gives me name.
How do I name a property of an object using a variable using JavaScript?
You can use this equivalent syntax:
obj[name] = value
Example:
let obj = {};
obj["the_key"] = "the_value";
or with ES6 features:
let key = "the_key";
let obj = {
[key]: "the_value",
};
in both examples, console.log(obj) will return: { the_key: 'the_value' }
With ECMAScript 2015 you can do it directly in object declaration using bracket notation:
var obj = {
[key]: value
}
Where key can be any sort of expression (e.g. a variable) returning a value:
var obj = {
['hello']: 'World',
[x + 2]: 42,
[someObject.getId()]: someVar
}
You can even make List of objects like this
var feeTypeList = [];
$('#feeTypeTable > tbody > tr').each(function (i, el) {
var feeType = {};
var $ID = $(this).find("input[id^=txtFeeType]").attr('id');
feeType["feeTypeID"] = $('#ddlTerm').val();
feeType["feeTypeName"] = $('#ddlProgram').val();
feeType["feeTypeDescription"] = $('#ddlBatch').val();
feeTypeList.push(feeType);
});
There are two different notations to access object properties
Dot notation: myObj.prop1
Bracket notation: myObj["prop1"]
Dot notation is fast and easy but you must use the actual property name explicitly. No substitution, variables, etc.
Bracket notation is open ended. It uses a string but you can produce the string using any legal js code. You may specify the string as literal (though in this case dot notation would read easier) or use a variable or calculate in some way.
So, these all set the myObj property named prop1 to the value Hello:
// quick easy-on-the-eye dot notation
myObj.prop1 = "Hello";
// brackets+literal
myObj["prop1"] = "Hello";
// using a variable
var x = "prop1";
myObj[x] = "Hello";
// calculate the accessor string in some weird way
var numList = [0,1,2];
myObj[ "prop" + numList[1] ] = "Hello";
Pitfalls:
myObj.[xxxx] = "Hello"; // wrong: mixed notations, syntax fail
myObj[prop1] = "Hello"; // wrong: this expects a variable called prop1
tl;dnr: If you want to compute or reference the key you must use bracket notation. If you are using the key explicitly, then use dot notation for simple clear code.
Note: there are some other good and correct answers but I personally found them a bit brief coming from a low familiarity with JS on-the-fly quirkiness. This might be useful to some people.
With lodash, you can create new object like this _.set:
obj = _.set({}, key, val);
Or you can set to existing object like this:
var existingObj = { a: 1 };
_.set(existingObj, 'a', 5); // existingObj will be: { a: 5 }
You should take care if you want to use dot (".") in your path, because lodash can set hierarchy, for example:
_.set({}, "a.b.c", "d"); // { "a": { "b": { "c": "d" } } }
First we need to define key as variable and then we need to assign as key as object., for example
var data = {key:'dynamic_key',value:'dynamic_value'}
var key = data.key;
var obj = { [key]: data.value}
console.log(obj)
Related to the subject, not specifically for jquery though. I used this in ec6 react projects, maybe helps someone:
this.setState({ [`${name}`]: value}, () => {
console.log("State updated: ", JSON.stringify(this.state[name]));
});
PS: Please mind the quote character.
With the advent of ES2015 Object.assign and computed property names the OP's code boils down to:
var obj = Object.assign.apply({}, $(itemsFromDom).map((i, el) => ({[el.id]: el.value})));
ajavascript have two type of annotation for fetching javascript Object properties:
Obj = {};
1) (.) annotation eg. Obj.id
this will only work if the object already have a property with name 'id'
2) ([]) annotation eg . Obj[id] here if the object does not have any property with name 'id',it will create a new property with name 'id'.
so for below example:
A new property will be created always when you write Obj[name].
And if the property already exist with the same name it will override it.
const obj = {}
jQuery(itemsFromDom).each(function() {
const element = jQuery(this)
const name = element.attr('id')
const value = element.attr('value')
// This will work
obj[name]= value;
})
If you want to add fields to an object dynamically, simplest way to do it is as follows:
let params = [
{ key: "k1", value: 1 },
{ key: "k2", value: 2 },
{ key: "k3", value: 3 },
];
let data = {};
for (let i = 0; i < params.length; i++) {
data[params[i].key] = params[i].value;
}
console.log(data); // -> { k1: 1, k2: 2, k3: 3 }
The 3 ways to access the object value
We can output the object value by passing in the appropriate key. Because I used emoji as the key in my example, it's a bit tricky. So let's look at a easier example.
let me = {
name: 'samantha',
};
// 1. Dot notation
me.name; // samantha
// 2. Bracket notation (string key)
me['name']; // samantha
// 3. Bracket notation (variable key)
let key = 'name';
me[key]; // samantha
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If you have object, you can make array of keys, than map through, and create new object from previous object keys, and values.
Object.keys(myObject)
.map(el =>{
const obj = {};
obj[el]=myObject[el].code;
console.log(obj);
});
objectname.newProperty = value;
const data = [{
name: 'BMW',
value: '25641'
}, {
name: 'Apple',
value: '45876'
},
{
name: 'Benz',
value: '65784'
},
{
name: 'Toyota',
value: '254'
}
]
const obj = {
carsList: [{
name: 'Ford',
value: '47563'
}, {
name: 'Toyota',
value: '254'
}],
pastriesList: [],
fruitsList: [{
name: 'Apple',
value: '45876'
}, {
name: 'Pineapple',
value: '84523'
}]
}
let keys = Object.keys(obj);
result = {};
for(key of keys){
let a = [...data,...obj[key]];
result[key] = a;
}

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