how to get key having special character(_) in object javascript

Question

I would like to know how to fetch the keys in object contains only underscore in javascript.

I would like to get the output with text before underscore, as shown

var obj={
  cn_start: "SG",
  cn_end:"TH", 
  cn1_start:"ML",
  cn1_end:"IN"
}

Expected Output

[
  cn, cn1
]

Answer 1

I believe using reduce is better, but for better readability, I use for loop. First, you get the keys using Object.keys, then iterate the keys finding the ones with '_' and push the prefix if it does not exists yet.

var obj={
  cn_start: "SG",
  cn_end:"TH", 
  cn1_start:"ML",
  cn1_end:"IN"
}

const keys = Object.keys(obj);
let underscoreKeys = [];
keys.forEach(key => {
  if(key.substring('_')){
    const prefix = key.split('_')[0];
    if(underscoreKeys.indexOf(prefix) < 0){
      underscoreKeys.push(prefix);
    }
  }
});

console.log(underscoreKeys);

Answer 2

For an Internet Explorer compatible answer, try the following:

var obj={
  cn_start: "SG",
  cn_end:"TH", 
  cn1_start:"ML",
  cn1_end:"IN"
}

var objkeys = Object.keys(obj);

var underscorekeys = [];

for(var i = 0; i < objkeys.length; i++) {
    var index = objkeys[i].indexOf("_");
    if(index > -1) {
        var prefix = objkeys[i].substr(0, index);
        if(underscorekeys.indexOf(prefix) < 0)
            underscorekeys.push(prefix);
    }
}

console.log(underscorekeys);

The other answers use 'arrow functions' or 'lambda functions' which is ES6 and not IE compatible .

Answer 3

You can grab the keys from your object using Object.keys() , then filter out all the keys which don't have an underscore in them. Next, you can .map() each key to a substring of itself by removing the underscore _ and its trailing text (using .replace(/_.+/, '') ). You can then use a new Set to remove any duplicates, and Array.from to turn that set back into an array:

 const obj={ cn_start: "SG", cn_end:"TH", cn1_start:"ML", cn1_end:"IN" } const get_keys = obj => Array.from(new Set(Object.keys(obj).filter(k => k.includes('_')).map(k => k.replace(/_.+/, '')))); console.log(get_keys(obj));

If you know all your keys will have an underscore in them, then you can remove the .filter() .

Answer 4

Split the key names by '_' and add them to Set to get unique keys.

 var obj = { cn_start: "SG", cn_end: "TH", cn1_start: "ML", cn1_end: "IN" }; const keys = [...new Set(Object.keys(obj).map(key => key.split("_")[0]))]; console.log(keys);

Answer 5

const keysNames = Object.keys(myObj);//returns the array ['keyName','keyName'];