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set.js

        var firebaseConfig = {
            apiKey: "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx",
            authDomain: "xxxxxxxxxxxxxxx.firebaseapp.com",
            databaseURL: "https://xxxxxxxxxxx.firebaseio.com",
            projectId: "xxxxxxxxxxxxxxxxx",
            storageBucket: "xxxxxxxxxxxxxxxxxxx.com",
            messagingSenderId: "xxxxxxxxxxxxxxxx",
            appId: "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx",
            measurementId: "xxxxxxxxxxxxxxxx"
        };

        temp = JSON.stringify(firebaseConfig);　//（１）JOSN形式に
        localStorage.setItem('firebaseConfig',temp);

get.js

        firebaseConfig1=localStorage.getItem('firebaseConfig')
        firebaseConfig2=JSON.parse(firebaseConfig1)　//（２）parse
        console.log(firebaseConfig2);