Good JS Interview Task

Symple Strings

/*
Have the function SimpleSymbols(str) take the str parameter being passed and determine if 
it is an acceptable sequence by either returning the string true or false. The str parameter 
will be composed of + and = symbols with several letters between them (ie. ++d+===+c++==a)
and for the string to be true each letter must be surrounded by a + symbol. So the string to the
left would be false. The string will not be empty and will have at least one letter. 
*/

var correctString = '+d+=3=+s+';
var incorrectString = '+d=+3=2+'

function SimpleSymbols(str){
	
	function symbolPositions(){
		return str.match(/[\d,a-z]/ig);		
	}
	
	function isNumber(symbol){
		return parseInt(symbol);
	}
	
	function checkSurroundings(symbol,surroundingSign){
		return str[str.indexOf(symbol) - 1] === surroundingSign && str[str.indexOf(symbol) + 1] === surroundingSign;
	}
	
	var positions = symbolPositions();
	for(var i = 0; i < positions.length; i++){
		
		if(isNumber(positions[i])){
			if(!checkSurroundings(positions[i],'=')){
				return false;
			}
		}else{
			if(!checkSurroundings(positions[i],'+')){
				return false;
			}
		}
	}
	
	return true;
}


console.log(SimpleSymbols(correctString));