将值与Javascript中数组中的所有值进行比较

Question

I am trying to make the following function run but I have stucked badly. I have an object "gidsAll" which I want to compare with each feature: feature.attributes.__gid.

The function is used in Openlayers for styling purpose of the features (points and lines). It is executed for each "feature.attributes.__gid" and what I want is to simple compare this value with all the values inside the "gidsAll". If the value matches one of the value in "gidsAll" then return green otherwise return red.

I think I need to use a loop somewhere but I can not make it work.

    var styleContext = {
            getColor: function (feature) {
            //alert(typeof(feature));//object
       // for (key in gidsAll){
            if (Math.round(feature.attributes.__gid) == Number(gidsAll)){
               return "green";
            } else {
                return "red";
            }   
        //} 
    }                           
};

Answer 1

You should check all the properties in the object before you return red , because you need to make sure there are no green matches. Note, that return "red" is outside the loop:

var styleContext = {
    getColor: function (feature) {

        for (key in gidsAll) {
            if (Math.round(feature.attributes.__gid) == Number(gidsAll)) {
                return "green";
            }
        }

        return "red";
    }
};

Answer 2

You can use Object.keys() to loop over all the objects properties.

Object.keys returns all the enumerable object's own properties of the object it receives.

 var styleContext = {
        getColor: function (feature) {
        var objectKeys = Object.keys(gidsAll);
        for (var i = 0; i < objectKeys.length; i++)
        {
           if (Math.round(feature.attributes.__gid) === parseInt(gidsAll[objectKeys[i]], 10)) 
           {
               return "green";
           }
        }
        return "red"; //nothing has been found
    //} 
}   

Answer 3

Just another version using ES5 Object.keys and Array.prototype.some methods:

var styleContext = {
  getColor: function (feature) {
    return Object.keys(gidsAll).some(function (p) {
      return Math.round(feature.attributes.__gid) == gidsAll[p];
    })? 'green' : 'red';
  }
};

If you do this a lot, use a loop as it's faster, but keys and some are concise.