JavaScript/Self Test

You can test yourself by answering the following questions. When in doubt, you should undertake a test in your development environment (editor, IDE, browser). So it's also a test of whether you have installed all the necessary tools to execute the examples of the Wikibook. __TOC__ Introduction {Inside which HTML element do you put the JavaScript code? |type="()"} - <javascript> - <source> + <script> - <scripting> - None of the above. {Does this sequence of statements lead to an error? let x = 0; x = 1; x = 'one'; |type="()"} - Yes || A variable can hold values of different types (at different times). + No || A variable can hold values of different types (at different times). Syntax and Semantic {Is there a syntax error? let x = 1: |type="()"} + Yes - No {Is there a syntax error? let x = 1; let y = 2; x+y = 3; |type="()"} + Yes - No {Which line contains a syntax error? /* 1 */ let x = 1; /* 2 */ let y = 1; /* 3 */ let x = 1, y = 1; /* 4 */ let x, y = 1; |type="()"} - Line 1 - Line 2 - Line 3 - Line 4 + None of the above {Which lines contain a syntax error? /* 1 */ let firstName_1 = "Michael"; /* 2 */ let firstName_2 = 'Michael'; /* 3 */ let firstName_4 = 'Mikhaïl'; /* 4 */ let firstName_5 = "Михаил"; |type="[]"} - Line 1 - Line 2 - Line 3 || It's perfectly correct when strings contain non-latin characters - Line 4 || It's perfectly correct when strings contain non-latin characters + None of the above {Which line leads to an error message? /* 1 */ let x = 1; /* 2 */ const y = 2; /* 3 */ x = 3; /* 4 */ y = 4; |type="()"} - Line 1 - Line 2 - Line 3 + Line 4 - None of the above {Which line leads to an error message? /* 1 */ let x = 1; /* 2 */ x = 2 + 3(4 + 5); /* 3 */ x = 3; /* 4 */ x = -x; |type="()"} - Line 1 + Line 2 || In opposition to usual algebra in mathematics, you cannot omit the multiply operator. - Line 3 - Line 4 || It's correct: like multiplication with -1. - None of the above {Which line(s) leads to an error message? /* 1 */ let x = [1, 2]; /* 2 */ let x = [[1], [2]]; /* 3 */ let x = [[1, 2], [3, 4]]; /* 4 */ let x = [[[1], [2]], [[3], [4]]]; /* 5 */ let x = [1], [2]; /* 6 */ let x = [1, '2']; |type="[]"} - Line 1 - Line 2 || It assigns an array to x. This array contains the two arrays [1] and [2] (containing one 'Number' each). - Line 3 - Line 4 + Line 5 - Line 6 - None of the above {Is there a syntax error? "use strict"; let persons = ['Alice', 'Bert', 'Caesar']; for (let i = 0, i < persons.length, i++) { alert(persons[i]); } // |type="()"} + Yes - No {Which line contains a syntax error? /* 1 */ alert("1 + 2 = " + 3); /* 2 */ alert("1 + 2 = " + "3"); /* 3 */ alert("1 + 2 = " 3) /* 4 */ alert(1 + 2 == 3) |type="()"} - Line 1 - Line 2 + Line 3 - Line 4 || The Numbers 1 and 2 are added. The result is compared with the Number 3. The comparison leads to a Boolean result. - None of the above Type Conversion {Which message(s) will not be shown? let x = 1, y = 2, z = '2'; alert(x + y); alert(x + z); alert(x - z); |type="[]"} - 3 - 12 - -1 || Depending on the context, the character '+' is an operator to add Numbers or to concatenate strings (possibly after type conversion). The character '-' subtracts Numbers (possibly after type conversion, which is what happens here). + All will be shown. || In the last line, a type conversion takes place. Then, the subtraction is performed. {What message(s) will not be shown? let x = 1; alert(x); alert(x = 5); alert(x == '5'); alert(x === 5); |type="[]"} + Error Message - true - false - 5 - 1 Loops {What will be the result in sum? "use strict"; let sum = 0; for (let i = 1; i < 5; i++) { sum = sum + i; } // alert(sum); |type="{}"} The result in sum will be { 10 _3 }. || Consider the cutting edges of the iteration: the first is 1, and the last is 4. {What will be the result in sum? "use strict"; let sum = 0; for (let i = 0; i < 5; i++) { for (let j = 10; j >= 0; j--) { if (i === j) { sum = sum + i - j + 1; } // } // } // alert(sum); |type="{}"} The result in sum will be { 5 _2 }. || The addition is only done when i is equal to j. Therefore i - j is always 0 and can be ignored. {Is there a syntactical error? "use strict"; let sum = 0; for (let i = 0; i < 5; i++) for (let j = 10; j >= 0; j--) { if (i === j) { sum = sum + i - j + 1; } // } // } // alert(sum); |type="()"} + Yes || The first for statement misses the { character but uses the }. Missing both is possible as long as the block consists of exactly 1 statement. - No || The first for statement misses the { character but uses the }. Missing both is possible as long as the block consists of exactly 1 statement. {What will be the result? "use strict"; let sum = 0; for (let i = 0; i = 3; i++) { sum = sum + i; } // alert(sum); |type="()"} - 0 - 6 + Infinite loop || The comparison operator is === or ==. The i = 3 is an assignment. JavaScript executes the assignment and interprets its result as true. - None of the above