JavaScript includes and indexOf not working in IE8

Question

Hi Everyone, 

 

I am working with one of the projects to make it compatible with IE8. I got this issue as I have shown below, will you please give me any alternate way or suggestion to use these functions in Javascript?

 

SCRIPT438: Object doesn't support property or method 'includes'

SCRIPT436: Object doesn't support property or method 'indexOf'  

 

 

I tried this  

function includes(container, value) {
    var returnValue = false;
    var pos = container.indexOf(value);
    if (pos >= 0) {
        returnValue = true;
    }
    return returnValue;
}

includes([1,2,3],2) //=> true
includes([1,2,3],'a') //=> false

Also tryed

if (!String.prototype.includes) {//To check browser supports or not
        String.prototype.includes = function (str) {//If not supported, then define the method
            return this.indexOf(str) !== -1;
        }
    }

but not work well for IE8.

 

Will anyone please help me.