cLitreKgValue 指向你尝试调用替换的地方，而不是字符串。在这种情况下，错误是正确的 - 数字没有替换方法。

I have this function:

function countLitreKgSums(cProductIds){
  var cLitreKgSums = new Array();
  var cWeek = 0;
  for(i=0;i<cProductIds.length;i++){
    var cLitreKgSum = 0;
    $("#plan_table td[class='week']").each(function(){
            cWeek = $(this).html();
            var cLitreKgValue = $("input[name*='plan_table_week" + cWeek + "_prod" + cProductIds[i] + "_']").val();
            if (cLitreKgValue == "") {
                cLitreKgValue = 0;
            }
            cLitreKgValue = cLitreKgValue.replace(/,/g, '.').replace(/[^\d\.]/g, '').replace(/\s/g, '');
            cLitreKgValue = parseFloat(cLitreKgValue);
            cLitreKgSum += cLitreKgValue;
       });
       cLitreKgSum = Math.round(cLitreKgSum * 100) / 100;
       cLitreKgSums[i] = cLitreKgSum;
  }
  return cLitreKgSums;
  //console.log(cLitreKgSums);
}

I get error message that .replace is not a function but in other functions it works as it should. What is the difference?

cLitreKgValue might be a number at the point where you try to call replace on it, not a string. In which case, the error is correct - numbers don't have a replace method.