Call JavaScript Constructor using an array for the arguments

Question

I have a constructor function in JavaScript as below and want to supply constructor arguments from an array:

 function dataRow(value1, value2, value3, value4, value5) {
                this.val1 = value1;
                this.val2 = value2;
                this.val3= value3;
                this.val4 = value4;               
                this.val5 = value5;
}

Now I want the constructor arguments supplied from an array:

var dataArray = new Array();

dataArray("Value1","Value2","Value3","Value4","Value5","Value6"...........)

I want (value1, value2, value3, value4, value5) this part to filled from my dataArray.

Also note that the overwhelming convention in JavaScript is that constructor function names start with a capital letter, to differentiate them from other non-constructor functions. — T.J. Crowder
– T.J. Crowder, Commented Jun 8, 2018 at 12:51

T.J. Crowder · Accepted Answer · 2018-06-08 15:19:01Z

6

In modern environments, you can use spread notation:

var row = new dataRow(...dataArray);

function dataRow(v1, v2, v3, v4, v5) {
  this.v1 = v1;
  this.v2 = v2;
  this.v3 = v3;
  this.v4 = v4;
  this.v5 = v5;
}

var dataArray = [1, 2, 3, 4, 5];
var row = new dataRow(...dataArray);
console.log(row.v1);
console.log(row.v2);
console.log(row.v3);
console.log(row.v4);
console.log(row.v5);

In older environments, it's a real pain to do this. In your specific case, probably just do it the hard way:

dataRow(dataArray[0], dataArray[1], dataArray[2], dataArray[3], dataArray[4]);

Or you can separate creation from the call, and call it with Function#apply:

var row = Object.create(dataRow.prototype);
dataRow.apply(row, dataArray);

function dataRow(v1, v2, v3, v4, v5) {
  this.v1 = v1;
  this.v2 = v2;
  this.v3 = v3;
  this.v4 = v4;
  this.v5 = v5;
}

var dataArray = [1, 2, 3, 4, 5];
var row = Object.create(dataRow.prototype);
dataRow.apply(row, dataArray);
console.log(row.v1);
console.log(row.v2);
console.log(row.v3);
console.log(row.v4);
console.log(row.v5);

That wouldn't work with a constructor created via class, but if you're creating it via class, use spread notation; they were introduced as the same time (ES2015).

I would suggest not doing this, though, especially in light of your comment below:

...how to create this dynamically this.val1 = value1; this.val2 = value2; this.val3= value3;...

Instead, use a single array property, and pass in an array which you either keep or copy:

function dataRow(values) {
  this.values = values;
  // or: this.values = values.slice();
  // to make a shallow copy
}

var dataArray = [1, 2, 3, 4, 5];
var row = new dataRow(dataArray);
console.log(row.values);

edited Jun 8, 2018 at 15:19

answered Jun 8, 2018 at 12:47

T.J. Crowder

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5 Comments

Kumar Warthak Over a year ago

Thank You for the reply i created below code from your suggestion function dataRow(){ } var row = Object.create(dataRow.prototype); dataRow.apply(row, dataArray); but its not working as well how to create this dynamically this.val1 = value1; this.val2 = value2; this.val3= value3;

T.J. Crowder Over a year ago

"but its not working" Yes, it works; see the live snippets above. "how to create this dynamically this.val1 = value1; this.val2 = value2; this.val3= value3;" Don't. Pass the array into the constructor, and then use an array: this.values = values; or this.values = values.slice(); if you want to (shallow) copy the passed-in array.

Kumar Warthak Over a year ago

I got your point: But in below code snippet i dont want to add the below code manually that is V1,v2,v3, this should be passed from array dynamically depending upon the number of items in a array variable as well i should be able pass this.v1 = v1; this.v2 = v2; this.v3 = v3; this.v4 = v4; from another variable function dataRow(v1, v2, v3, v4, v5) { this.v1 = v1; this.v2 = v2; this.v3 = v3; this.v4 = v4; this.v5 = v5; }

T.J. Crowder Over a year ago

@KumarWarthak - If you pass in the array, you can do string concatenation to create the property names: value.forEach((value, index) => this["v" + (index + 1)] = value; }). But I wouldn't.

Kumar Warthak Over a year ago

If i have a two dataarray like: dataarray =["Value1","Value2","Value3","Value4","Value5","Value6"...........] dataarray1=["this.Value1 = v1;,this.Value2 = v1;,this.Value3 = v1;,this.Value4= v1;, "] i want to use it as below: function dataRow(dataarray) { dataarray1 }

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