The World’s Most Misunderstood Programming Language. Douglas Crockford
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//if first is obj, javascript return second var obj={ amir:'my strting'; } var value= obj && 0; console.log(value); //0 //if first is boolean, javascript return second var value= true && obj; console.log(value); //object {amir:'mystring'}; //if one of them is null, answer is null var value='Z' && null console.log(value); //null //if one of theme is undefined or NaN, answer is NaN or undefined var value = 'M' && undefined console.log(value); //undefined //if first is false ,javascript ignore next and return false var value = false && 'Z'; console.log(value); //false var value = true && true; console.log(value); //true var value = true && false; console.log(value); //false var value = false && true; console.log(value); //false var value = false && false; console.log(value); //false var value = obj && 99; console.log(value); //99 var value= !" "; console.log(value); //false var value= !""; console.log(value); //true var value= !NaN; console.log(value); //true var value= !undefined; console.log(value); //true var value= !0; console.log(value); //true var value= !99; console.log(value); //false var value= !!false; console.log(value); //false var value= !'A'; console.log(value); //false var value= !undefined; console.log(value); //true var value= !new Object(); console.log(value); //false var value= !null; console.log(value); //true //if first is obj ,javascript return obj var value = obj || 'Z'; console.log(value); //object {amir:'mystring'} //if first is false ,javascript return second var value = false || 'Z'; console.log(value); //Z |