IT Course JavaScript Basics 039_Type Conversion

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let num = 5 + "5";
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console.log(num);  // Output "55", when adding a number and a string, the number is converted to a string

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let num = 123;
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let str1 = String(num);  // String() function, can handle `null` or `undefined`
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let str2 = num.toString(); // toString() method, cannot handle `null` or `undefined`
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let str3 = num + ""; // By adding an empty string, get implicit type conversion to string
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console.log(str1);  // Output "123"
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console.log(str2);  // Output "123"
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console.log(str3);  // Output "123"

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let str1 = "123";
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let str2 = "";
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let str3 = "aaa";
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let num1 = Number(str1);
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let num2 = Number(str2);
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let num3 = Number(str3);
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let num4 = +str1;
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console.log(num1);  // Output 123
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console.log(num2);  // Output 0
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console.log(num3);  // Output NaN
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console.log(num3);  // Output 123, if using - sign, output -123

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let str = "42";
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let num = parseInt(str);
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console.log(num);  // Output 42
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let str = "3.14";
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let num = parseFloat(str);
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console.log(num);  // Output 3.14

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let value = "Hello";
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let bool1 = Boolean(value);
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let bool2 = !value;
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console.log(bool1);  // Output true, non-empty string converts to true
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console.log(bool2);  // Output true, use logical NOT for implicit conversion of non-boolean values (! value is false, then use !! to get positive)