function isEmpty(obj){ if(typeof obj == "undefined" || obj == null || obj == ""){ return true; }else{ return false; } } 1. 2. 3. 4. 5. 6. 7. 参考二: if (variable1 !== null || variable1 !== undefined || variable1 !== '') { var variable2 = variable1; } 1...
The result is false if the argument is the empty String (its length is zero); otherwise the result is true Quote taken fromhttp://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf One caveat警告 is thatnew String("")is truthy! This is because it is an object, whereas ...
a== b;//truea ==null;//trueb ==null;//truea ==false;//falseb ==false;//falsea == "";//falseb == "";//falsea == 0;//falseb == 0;//false null 和 undefined 之间的强制类型转换是安全可靠的,上例中除 null 和 undefined 以外的 其他值均无法得到假阳(false positive)结果。个...
Boolean: true or false Number: 1, 6.7, 0xFF String: "Gorilla and banana" Symbol: Symbol("name") (starting ES2015) Null: null Undefined: undefined. And a separatedobject type: {name: "Dmitri"}, ["apple", "orange"]. 从6个基本类型undefined是一个特殊的值,它的类型为Undefined。根据[ECMA...
The Falsy values 0, “” (empty string) and false are equal to each other and comparison among them results in a true value. Null and undefined are both falsy values but are not equal to any value, not even falsy. A bit strange but that’s true. Null and undefined are equal to the...
Number(true)// returns 1 Converting Booleans to Strings The global methodString()can convert booleans to strings. String(false)// returns "false" String(true)// returns "true" The Boolean methodtoString()does the same. false.toString()// returns "false" ...
“Control character in string: {a}.” : “在字符串中出现了Control的字符”, “Avoid \\’.” : “避免 \\”, “Avoid \\v.” : “避免 \\v”, “Avoid \\x-.” : “避免 \\x-”, “Bad escapement.” : “错误的转义字符”, ...
Boolean: true or false Number: 1, 6.7, 0xFF String: "Gorilla and banana" Symbol: Symbol("name") (starting ES2015) Null: null Undefined: undefined. And a separated object type: {name: "Dmitri"}, ["apple", "orange"].从6个基本类型undefined是一个特殊的值,它的类型为Undefined。根据[ECMA...
false ?? 'bar' // false 1.3 注意 不可以将 ?? 与 AND(&&)OR(||)一起使用,会报错。 null || undefined ?? "foo"; // 抛出 SyntaxError true || undefined ?? "foo"; // 抛出 SyntaxError 二、可选链 Optional chaining 2.1 介绍 可选链操作符(?.)允许读取位于连接对象链深处的属性的值,而不...
typeof"John"// Returns string typeof("John"+"Doe")// Returns string typeof3.14// Returns number typeof33// Returns number typeof(33+66)// Returns number typeoftrue// Returns boolean typeoffalse// Returns boolean typeof1234n// Returns bigint ...