Create a polygon from an array of coordinates in arcgis javascript api

You could use a textarea to collect pairs of coordinates. The coordinates should have a comma between them and each pair should be separated by a new line. Then format the pairs to look like:

[[[coord1,coord2],[coord3,coord4],[coord5,coord6]]]

Here is an example of how to do that:

HTML

<textarea id='textareaID'></textarea>

JavaScript

var arrayOfCoordinates = document.getElementById('textareaID').value.split('\n');

for(i=0;i<arrayOfCoordinates.length;i++){
    arrayOfCoordinates[i] = arrayOfCoordinates[i].replace(/,/g, "],[");
}
arrayOfCoordinates = JSON.parse("[[[" + arrayOfCoordinates + "]]]")

Here is the code required (from the ESRI Javascript API) to create a new graphic using JSON. Pass in your arrayOfCoordinates variable as your rings and the wkid for your map's spatial reference. Then use your map object to add the graphic with map.graphic.add(graphic).

require([
  "esri/graphic" 
], function(Graphic) {
  var myPolygon = {"geometry":{"rings":arrayOfCoordinates,"spatialReference":{"wkid":26191}},
    "symbol":{"color":[0,0,0,64],"outline":{"color":[0,0,0,255],
    "width":1,"type":"esriSLS","style":"esriSLSSolid"},
    "type":"esriSFS","style":"esriSFSSolid"}};
  var gra = new Graphic(myPolygon);

map.graphics.add(gra);
});