在Javascript中对对象属性执行字符串方法

Question

Whenever I try to perform string operations on variables that contain the values of object's properties in Javascript, I get an error about the interpreter not being able to find whatever the method Im trying to use for that object:

var arrOfEntries = {};

arrOfEntries["name1"] = "Jane" ;
arrOfEntries["age1"] = "40" ;
arrOfEntries["name2"] = "Kathy" ;
arrOfEntries["age2"] = "35" ;
arrOfEntries["name3"] = "Mary" ;
arrOfEntries["age3"] = "23" ;
arrOfEntries["name4"] = "Donna" ;
arrOfEntries["age4"] = "32" ;

var result = ' ';
for (prop in arrOfEntries) {
    var tempVar = String(prop) /*/this line was added as an attempt to force the property into the type String, but does not work*
    if (tempVar.includes("name"))
        result += tempVar
    }

In this case, I simply wish to check for the existence of the string "name" within the name of each property of that object and then collect only these properties for further actions. What am I missing here?

Answer 1

prop is already a string. You should just need this:

for (prop in arrOfEntries) {
    if (arrOfEntries.hasOwnProperty(prop) && prop.indexOf("name") !== -1) {
        result += arrOfEntries[prop];
    }
}

I added hasOwnProperty so that you wouldn't erroneously try and add a method that already exists on the Object type.

Also just FYI: arrOfEntries is an object (with string/value keys), not an array - there is some distinction in JavaScript types.

Answer 2

Use largerString.indexOf("substring") , as includes() does not have wide browser support.

The indexOf() method will tell you the starting position (as an integer) of the first match of substring within largerString . If no matches were found, it returns -1

See below:

var arrOfEntries = {};

arrOfEntries["name1"] = "Jane" ;
arrOfEntries["age1"] = "40" ;
arrOfEntries["name2"] = "Kathy" ;
arrOfEntries["age2"] = "35" ;
arrOfEntries["name3"] = "Mary" ;
arrOfEntries["age3"] = "23" ;
arrOfEntries["name4"] = "Donna" ;
arrOfEntries["age4"] = "32" ;

var result = ' ';
for (prop in arrOfEntries) {
    if (prop.indexOf("name") >= 0) {
        result += prop
    }
}

If you do a console.log(result) you will get "name1name2name3name4"

Answer 3

Do sth like that:

var arrOfEntries = {};
arrOfEntries["name1"] = "Jane" ; arrOfEntries["age1"] = "40" ;
arrOfEntries["name2"] = "Kathy" ; arrOfEntries["age2"] = "35" ;
arrOfEntries["name3"] = "Mary" ; arrOfEntries["age3"] = "23" ;
arrOfEntries["name4"] = "Donna" ; arrOfEntries["age4"] = "32" ;
var result = ' ';
for (prop in arrOfEntries) {
if (prop.indexOf('name') != -1)
{
 alert(arrOfEntries[prop]);
}
}

Greetz

Answer 4

You have several issues:

1. You're trying to force the value into a string by using var tempVar = String(prop) which isn't going to work because you left out the new operator. It should be var tempVar = new String(prop); . You can ignore it though since it's not needed.

2. String.prototype.includes was introduced in ES6 and doesn't have wide browser support yet. Check the documentation at https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/includes for more details.

3. Considering the lack of support for includes , you can use indexOf as a replacement: if (prop.indexOf('name') >= 0) { // 'name' is included }