SOURCE

let message = "some string";
console.log(typeof message);   // "string"
console.log(typeof age)     // undefined
console.log(typeof true)     // boolean
console.log(typeof 95);        // "number" 
console.log(typeof null)     // object
console.log(typeof undefined)  //undefined
console.log(typeof NaN)     // number
console.log(null == undefined)  //ture
console.log(null === undefined)  //false
console.log(0.1+0.2)            // 精度丢失
console.log(0/0)                // NaN
console.log(5/0)               // Infinity
console.log(NaN == NaN)        // false
console.log(isNaN(NaN));     // true
console.log(isNaN(10));      // false - 10 is a number
console.log(isNaN("10"));    // false - can be converted to number 10
console.log(isNaN("blue"));  // true - cannot be converted to a number
console.log(isNaN(true));    // false - can be converted to number 1
console 命令行工具 X clear

                    
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console