Combining inner json array with space and outer with newline

You could use Array#map for the outer array with the line feed and Array#join with ' ' for inner and with '\n' for outer arrays.

var array = [
        [["a"], ["t"]],
        [["b"], ["t"]],
        [["c"], ["t"]]
    ],
    result = array.map(function (a) { 
        return a.join(' ');
    }).join('\n');

console.log(result);

ES6

var array = [
        [["a"], ["t"]],
        [["b"], ["t"]],
        [["c"], ["t"]]
    ],
    result = array.map(a => a.join(' ')).join('\n');

console.log(result);

Join function does not work for nested array. You can use following way to handle such situation.

var array = [
    [    ["a"],    ["t"]    ], 
    [    ["b"],    ["t"]    ],
    [    ["c"],    ["t"]    ]
    ];

    for (var i=0, l=array.length; i<l; i++){
        if (array[i] instanceof Array){
            array[i] = array[i].join(" ");
        }
    }
    var energy = array.join('\n');

All array methods are fancy but may be you can still simply do like

var arr = [[["a"],["t"]],
           [["b"],["t"]],
           [["c"],["t"]]
          ],
 result = arr.join("\n").replace(/,/g," ");
console.log(result);