string.endswith(“”) does not work in IE(not sure how to use a Polyfill)

Question

I am using string.endswith() to loop through JSON objects and find out if the any property of the object endswith a "Value" substring.

After finding out if the the object property ends with "Value" , i am trying to round off the value of the property to 2 decimals which are by default 5 decimals.

Here is my code

var MyObj= [{"$id":"1","GeoName":"EAST","ReachValue":87.88221970554928,"ReachValue":90.71955219607294,"DepthValue":18.44377295716579,"ShareValue":16.732108234801206},{"$id":"2","GeoName":"WEST","ReachValue":87.88221970554928,"ReachValue":90.71955219607294,"DepthValue":18.44377295716579,"ShareValue":16.732108234801206}];
Obj = JSON.parse(JSON.stringify(MyObj)).map(function (e) {
            return Object.keys(e).reduce(function (p, n) {
                if (n.endsWith("Value"))
                    p[n] = Math.round(e[n] * 100) / 100;
                else
                    p[n] = e[n];
                return p;
            }, {})
        });

The above code works absolutely fine in chrome and Firefox , While IE it throws endsWith is not a function exception.

I found out for such issues pollyfills are used, which i tried and i failed. I am not even sure if i used the pollyfill correctly.

so here is how i did it,

function polyFillEndswith(searchString, position) {
            if (!String.prototype.endsWith) {
                String.prototype.endsWith = function (searchString, position) {
                    var subjectString = this.toString();
                    if (typeof position !== 'number' || !isFinite(position) || Math.floor(position) !== position || position > subjectString.length) {
                        position = subjectString.length;
                    }
                    position -= searchString.length;
                    var lastIndex = subjectString.lastIndexOf(searchString, position);
                    return lastIndex !== -1 && lastIndex === position;
                }
            }
        }

Obj = JSON.parse(JSON.stringify(BubbleObj)).map(function (e) {
                return Object.keys(e).reduce(function (p, n) {
                    if (n.polyFillEndswith("Value", "0"))
                        p[n] = Math.round(e[n] * 100) / 100;
                    else
                        p[n] = e[n];
                    return p;
                }, {})
            });

is the above code even correct? if not how can i change it to achieve my objective?

Answer 1

The polyfill function you have is actually for attaching the endsWith function to the native String object, which JavaScript allows you to do. It will allow you to call endsWith like normal.

Instead of wrapping it in a function, let it run right away, then just use the normal endsWith :

if (!String.prototype.endsWith) {
    String.prototype.endsWith = function (searchString, position) {
        var subjectString = this.toString();
        if (typeof position !== 'number' || !isFinite(position) || Math.floor(position) !== position || position > subjectString.length) {
            position = subjectString.length;
        }
        position -= searchString.length;
        var lastIndex = subjectString.lastIndexOf(searchString, position);
        return lastIndex !== -1 && lastIndex === position;
    }
}

Obj = JSON.parse(JSON.stringify(BubbleObj)).map(function (e) {
    return Object.keys(e).reduce(function (p, n) {
        if (n.endsWith("Value"))
            p[n] = Math.round(e[n] * 100) / 100;
        else
            p[n] = e[n];
        return p;
    }, {})
});

Answer 2

You implemented the polyfill incorrectly.

You just need to include somewhere before using your endsWith function.

if (!String.prototype.endsWith) {
  String.prototype.endsWith = function(searchString, position) {
      var subjectString = this.toString();
      if (typeof position !== 'number' || !isFinite(position) || Math.floor(position) !== position || position > subjectString.length) {
        position = subjectString.length;
      }
      position -= searchString.length;
      var lastIndex = subjectString.lastIndexOf(searchString, position);
      return lastIndex !== -1 && lastIndex === position;
  };
}

Line 1 checks whether you need a polyfill. On line 2, the function is assigned to String.prototype.endsWith , which means it can be called with String.endsWith(searchString, position)

Answer 3

Given requirement you can use String.prototype.slice() with parameter -5

if (n.slice(-5) === "Value")

or RegExp.prototype.test() with RegExp /Value$/

if (/Value$/.test(n))