JavaScript数据类型转换——转成Boolean类型

将需要转换的数据传递给Boolean()函数

• 对于字符串而言: 只要不是空字符串(没有任何内容),只要字符串中有内容(包含空格/Table) 都会转换为true

    var str1 = "";  // "" --> false
    var str2 = " "; // " " --> true;
    var str3 = "abc"; // " " --> true;
    var res1 = Boolean(str1);
    console.log(res1);

    var res2 = Boolean(str2);
    console.log(res2);

    var res3 = Boolean(str3);
    console.log(res3);

• 对于Number类型而言: 只要不是0都会转换为true, 只有0会转换为false

    var num1 = 0;
    var num2 = -1;
    var num3 = 1;
    var res1 = Boolean(num1);
    console.log(res1);        //false
    var res2 = Boolean(num2);  
    console.log(res2);        //true
    var res3 = Boolean(num3); 
    console.log(res3);        //true

• 对于null和undefined而言, 都会转换为false

    var n = null;
    var u = undefined;
    var res1 = Boolean(n);
    console.log(res1);  //false
    var res2 = Boolean(u);
    console.log(res2);  //false

• 对于NaN也会转换为false

    var value = NaN;
    var res3 = Boolean(value);
    console.log(res3);  //false

• 总结:
  "" / 0 / null / undefined / NaN --> false