Your code has several syntax errors (unbalanced quotes, mismatching quotes, trailing & without quotes, …), and variables that have not been defined with var, let or const. It assigns to key_for_url, but never uses that value. It references a “slug” property, but that doesn’t exist in your input data. It assumes a certain key order in plain objects, as it uses indexOf on Object.keys. This is a code smell. Variable names json1 and json2 are not very descriptive.

Here is code you could use:

let filter = {
  "sku Brand": "abc",
  "strngth": "ALL",
  "area": "",
  "Country": "",
  "local Brand": "",
  "theme": "HideDisNameFilters"
}

let tabs = {
  "nav": [{
      "tabname": "tab1",
      "exclude": ["area", "xyz"]
    },
    {
      "tabname": "tab2",
      "exclude": ["Country"]
    }
  ]
}

let result = tabs.nav.map(({tabname, exclude}) =>
  `<a href='${
    Object.entries(filter)
      .filter(([key]) => !exclude.includes(key) && key != "theme")
      .map(([key, value]) => `${key}=${value}`)
      .join("&")
  }' target='_blank'>${tabname}</a>`
);

console.log(result);

Solution:

obj1 is an array, so the loop will be obj1.forEach and accessing the value will be prop[‘exclude’].
I have made the code a bit more short.

    json1 = {
        "sku Brand": "abc",
        "strngth": "ALL",
        "area": "",
        "Country": "",
        "local Brand": "",
        "theme": "HideDisNameFilters"
    }

    json2 = {
        "nav": [{
                "tabname": "tab1",
                "exclude": ["area", "xyz"]
            },
            {
                "tabname": "tab2",
                "exclude": ["Country"]
            }
        ]
    }

    final_array = []

    var obj1 = json2.nav;
    obj1.forEach(function (prop) {

        let str = "";
        
        Object.keys(json1).forEach((key) => {
            if (!prop['exclude'].includes(key) && key !== 'theme') {
                newKey = key.split(' ').join('+');
                str = str + newKey + '=' + json1[key] + "&";
            }
        })

        var t1 = "<a href=" + "'" + str + "'" +  " target = '_blank' > "+ prop['tabname'] +" < /a>"
        final_array.push(t1)

    });

    
    console.log(final_array)

Am having the arrays,

Now i need to get all tab names looping through and exclude the values present in exclude.

          json1  ={
        "sku Brand": "abc",
        "strngth": "ALL",
        "area": "",
        "Country": "",
        "local Brand": "",
        "theme": "HideDisNameFilters"
    }

    json2 = {
         "nav": [{
         "tabname": "tab1",
         "exclude':["area',"xyz"]
          },
          {
         "tabname": "tab2",
         "exclude":["Country"]
          }
            ]}

    var obj1 = json2.nav;
    console.log(obj1)
 Object.keys(obj1).forEach(function(prop) {
      var str1  = "";
      var maxLength =  Object.keys(json1).length-2
      Object.keys(json1).forEach(key => {
        var str  = "";
        var t1 = "";
        var index =  Object.keys(json1).indexOf(key);
        if(key != "theme"){
        if(!obj1[prop]['exclude'].includes(key)){
      str = key + "="+ json1[key];

          str1 +=str&
          console.log("str",str, " = ",str1 )
        if(maxLength == index){
         var t1 = "<a href="+str1 + "target='_blank'>"+ obj1[prop]['tabname'] +"</a>"
         final_array.push(t1)
        }
        }
        }
      });
      
    });

o/p should be: (it will exclude and form the url by checking from exclude array as below)

["<a href='sku+Brand=abc&Strngth=ALL&Country=&local+Brand=&' "target='_blank'>tab1<a>,"<a href='sku+Brand=abc&Strngth=ALL&area=&local+Brand=&' "target='_blank'>tab2<a>"]

AM not getting the correct output as expected…