Edit in JSFiddle

var s1 = 'hello',
    s2 = new String('hello'),
    
    concat1 = s1 === s1 + '',
    concat2 = s2 === s2 + '',

    toString1 = Object.prototype.toString.call(s1) === '[object String]',
    toString2 = Object.prototype.toString.call(s2) === '[object String]',

    typeOf1 = typeof s1 == 'string',
    typeOf2 = typeof s2 == 'string',

    instanceOf1 = s1 instanceof String,
    instanceOf2 = s2 instanceof String,

    typeOfInstanceOf1 = typeof s1 === 'string' || s1 instanceof String,
    typeOfInstanceOf2 = typeof s2 === 'string' || s2 instanceof String;

document.getElementById('result').innerText =
    'concat1 = ' + concat1.toString() + '\n' +
    'concat2 = ' + concat2.toString() + '\n' +
    'toString1 = ' + toString1.toString() + '\n' +
    'toString2 = ' + toString2.toString() + '\n' +
    'typeOf1 = ' + typeOf1.toString() + '\n' +
    'typeOf2 = ' + typeOf2.toString() + '\n' +
    'instanceOf1 = ' + instanceOf1.toString() + '\n' +
    'instanceOf2 = ' + instanceOf2.toString() + '\n' +
    'typeOfInstanceOf1 = ' + typeOfInstanceOf1.toString() + '\n' +
    'typeOfInstanceOf2 = ' + typeOfInstanceOf2.toString() + '\n';
<pre id="result"></pre>