How to concatenate strings without using eval?

Question

How do I concatenate these strings to get value from a variable. I want to avoid eval as so many of you are not keen on its use.

function getLesson() {
    var lesson = "lesson" + localStorage.lessonNGS;
    document.getElementById("lessonNumber").innerHTML = "Lesson " + (eval(lesson + "." + number));
    document.getElementById("lessonTitle").innerHTML = (eval(lesson + "." + title));
    document.getElementById("lessonScore").src = (eval(lesson + "." + score));
    document.getElementById("mp3").src = (eval(lesson + "." + trackmp3));
    document.getElementById("ogg").src = (eval(lesson + "." + trackogg));
    document.getElementById("lessonTrack").load();
}

This works but I'm told it will cause me conflicts in some browsers.

CodeWizard · Accepted Answer · 2015-12-29 07:49:31Z

3

Simply remove the eval

// Demo data
localStorage.setItem("lessonNGS",1);

var lesson1 = {
    number: "1",
    title: "Quarter Notes",
    score: "scores/01_quarternotes.jpg",
    trackmp3: "tracks/mp3/01_quarternotekeyexercises.mp3",
    trackogg: "tracks/ogg/01_quarternotekeyexercises.ogg"
};

function getLesson() {
    debugger;
    var lesson = window["lesson" + localStorage.lessonNGS];
    document.getElementById("lessonNumber").innerHTML = "Lesson " + lesson.number;
    document.getElementById("lessonTitle").innerHTML = lesson.title;
    document.getElementById("lessonScore").src = lesson.score;
    document.getElementById("mp3").src = lesson.trackmp3;
    document.getElementById("ogg").src = lesson.trackogg;
    document.getElementById("lessonTrack").load();
}

edited Dec 29, 2015 at 7:49

answered Dec 29, 2015 at 7:17

CodeWizard

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5 Comments

Phil Over a year ago

Thanks, but the variable lesson isa string which is the name of a global variable that I want the first array of number from. So I want the value of lesson1("number") to add to the string to make "Lesson 1" for example.

CodeWizard Over a year ago

i dont understand. the lesson is an array?

Phil Over a year ago

var lesson1 = {number:"1", title:"Quarter Notes", score:"scores/01_quarternotes.jpg", trackmp3:"tracks/mp3/01_quarternotekeyexercises.mp3", trackogg:"tracks/ogg/01_quarternotekeyexercises.ogg"};

CodeWizard Over a year ago

Ok got you, updating the answer accordinaly

Phil Over a year ago

The variable lesson in the function is a carrier for the text "lesson1" made my appending the local storage variable, which is the lesson the student most recently used. There 39 lessons, whose variables are kept in a series of the above styled object arrays. The function fills the page with the title, music score and music track.

Bek · Accepted Answer · 2015-12-29 08:50:57Z

2

Javascript String.prototype.concat():

str.concat(string2, string3[, ..., stringN])

Example:

var hello = 'Hello, ';
console.log(hello.concat('Kevin', ' have a nice day.'));

edited Dec 29, 2015 at 8:50

Bek

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answered Dec 29, 2015 at 7:18

Lavi Avigdor

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